Hi Chiromum,
excuse the length of the post, I hope it will be worth it for some people, since we had serious trouble finding any useful information on tramping with babies or toddlers when we started.
Can't seem to see how old your post is but will answer anyway - maybe you can share what experiences you had in the meantime?
First off: Never, ever, understimate what babies, toddlers, and children can do, in many ways! If you give them the opportunity, they will surprise you many times, and have a ball doing it.
"Second off", of course: Never, ever put anything above looking after your little ones, and don't foregt it for a second, round the clock - warm, dry, drink, food, bum, mood. It's only fair to do that.
Look at native peoples around the world in all sorts of environments, with very limited equipment, and at what they do with their whole family no matter what age, and you quickly realise that it's not the children who define the limits. It's the parents and their knowledge, skill, experience; and their relationship to their little ones.
Most people, including most trampers, seem to think that what we do is quite extreme, either because they think it's dangerous (more about that later), or stressful, or both - but truthfully and speaking from experience, it's neither if you do it right. We braced for a tough experience when we started it, but that never really came - of course you need to think differently, but it's in fact pretty easy, at least for us, to the point that we really REALLY can't believe how many tramping-parents do not go on these wonderful trips with their little ones! It's like breaking through a wall, once you've started and you have your head on the other side, you realise that the wall wasn't half as thick as you thought, and the other side is actually a really nice place. There are much, much more hardcore trampers than us - lots of them - and we are convinced that if we can do this and enjoy it, loads of other people can as well. All you need is a reasonable amount of tramping experience, and then add to that some thinking outside the box and a good relationship with your baby / toddler. Many people who see us seem to think we're oh so tough and "doing it all for our baby", while we're actually having a really good and quite cruisy time - but when we tell them, they think we're putting on a show. It's just so uncommon that many people simply can't believe that it should be possible, let alone enjoyable. Don't listen to the naysayers! Try it, and you will never look back. Just use your brain while you do it.
We've been doing day trips and overnighters with our baby within his first few months of life; this summer we've been out around the Routeburn area for 8 days autonomously, meaning we were carrying all food and fuel and other supplies, didn't use huts or camp sites, and camped in the bush with a tarp. It was bucketing down on us most of the time and was stormy on some days, but we were warm, well fed, and safe without exception.
Most of our tramping-with-baby-strategy worked well, a few things we do differently now. We borrow lots of ideas from the ultralight community, but don't consider ourselves ultralight, and have a strong emphasis on "going safe", meaning within our abilities and well equipped for the worst possible conditions.
For eight days out, including 12 kg of our toddler, we usually start with a pack weight of around 24 kg each, which is not too bad considering that the food goes down day by day, and the little one starts to walk up to an hour or more each day now as well.
We could go lighter, but don't; we prefer to still be able to smile even in the worst weather. The rain washed most other trampers without children out of that area while we were there, while we really had a good time - even though some more sunshine would have been nice.
If you want to try it for the first time, if you can it can help to take a friend or relative along who MUST be totally committed to help with everything. Not so much for sharing the weight, but an extra pair of hands helps heaps. If that friend is throwing pebbles into a creek, the other two can pitch the tarp / tent in terrible weather much more easily, for example.
Talking of weather: You MUST have a baby carrier that has a very solid rain- and storm proof rain cover all round, and your little one MUST have full polypro AND rain suit. With that, you're pretty much sorted regarding warmth. Goes without saying, taking cotton is asking for very, very serious trouble, don't even think about it, not one piece.
Once baby can sit upright properly for a longer time, a back carrier is the way to go. Before that, use a front carrier or moby wrap. Macpac makes a front carrier that can be detached from its own carrying harness (the adult side) and clicked into the standard harness of a normal backpack, by the way - they don't advertise that fact, but it works perfectly and is safe.
We slept under a quilt, with him between us - as we share two queen-size mattresses that are put together at home as well, nothing he wasn't used to before, no problem. Try a night in your garden before maybe if you're unsure. He always loves to go to bed underneath the tarp though, hard to keep him out of it, and loves the camp mats as well.
One rule of thumb is: Take more time. Often we were surprised at how far we would get in a day, as our toddler was enjoying himself silly almost all the time, and the mood of the little one is directly related to what you can do. But sometimes things just don't work as planned, and it's important to be able to stop and call it a day soon when that happens, not be frustrated about it, and just enjoy being where you are with your children. That also seems to be the trick to make sure that he wants to go again and again - works for us - at least so far, knock on wood!
In our experience, even little toddlers are much more adaptable to backcountry situations than most adults seem to be - as long as you keep them warm, well fed, dry (with the exception of feet sometimes, but that's what superwarm socks are for), and: Make them part of everything! As long as he could help pushing pegs into the ground, doing dishes, getting water etc. pp., he felt he was a real member of the family, and was SO proud and happy! Also, give him a collapsed tramping pole, and he walks like crazy for up to an hour and a half or more.
Of course, people told us before that "it can't be done", "it's dangerous and irresponsible" etc. pp., and some people still tell us now. But none of them has actually seen how we do out there - if they had, they would probably agree that the way we do it it's not more dangerous than spending a day in the city with our toddler. It also is, for example, WAY (!!!) safer than cycling in say Christchurch or Auckland, with our without baby. Yet not many people realise just how dangerous doing that is. That is not an exaggeration at all - it really depends on how you do it, both of it. If you cross streets like an idiot, you do get run over. If you go to the mountains ill equipped or without enough experience etc. pp., you can have bad outcomes as well. It really depends much more on how you do it than on what you do. As a healthy parent, your guts will always tell you where the line is, if you listen to them. Respect that instinct, it's a good one.
A general part of any good baby tramping strategy is: Make absolutely every single task that you need or may need to do as little time consuming as possible. That drastically increases your ability to respond to situational changes and circumstances. If your little one(s) suddenly need to stop to play with some rocks because they won't sit in the carrier anymore, it's great if you can quickly and without many complicated things to do cook dinner, for example - right there on the trailside - and if they suddenly decide to want to go on again, change your plan again, NOT eat it, but pack it up in a tupperware thingy or similar, wrap it in your sleeping bag, and eat it at night at camp where it's still warm. Just as an example, you get my point.
UMBRELLAS, the larger the better, may seem odd and heavy - compare! - but they buy time galore in many situations as instant shelters. Lunch stop, nappy change, map reading, whatever - not only great for the offspring, but also for you.
Basically, anything that helps keep everybody in high spirits, and anything that helps save time and hassle, is worth some extra weight multiple times. Look for those solutions. Once you start tramping with your toddler(s), you will identify them all the time. Tip: Take a pen and piece of paper, have it readily accessible all the time. On our first trips, I scribbled about half a page of notes per day, and did some serious improving of our gear back home. Without pen and paper, would hav forgotten half of it.
One particular thing we do and recommend: Take an emergency beacon. They are no substitute for anything else, but add quite a decent time advantage in most situations where you do need external help. We've never needed it, never even come close, but wouldn't go without it. They can be rented from several places in town, and even locally from businesses sometimes, often even on short notice - pays to ask ahead though. For some dollars per day, it's a no-brainer.
People have travelled long distances on foot with their babies, toddlers and children for millennia - with the ridiculously powerful equipment that is available today, with some bush skills and good common sense, there is absolutely no reason why we shouldn't do the same.
Ramble ramble - sorry! Hope that was interesting for some people. Would be really cool to meet some other young families in the mountains some time!!!
Cheers,
Matt