Like others my wife and I had our now 4 1/2 year old out beginning at two weeks, at a year did a two month camping trip through BC and Alberta with consistent snow showers. We utilized a dog bed rather than the pak-n-play that others reference. This established the fact that the dogs can sleep with the kids, keep the kids warm, and is an overall great place for a kid to sleep.
We also grabbed
Tuffo suits which are bomber in any weather, but aren't breathable so if you layer your kids well they will stay exceptionally warm.
The 4 1/2 year old now sleep in a
Duster and we picked another up for the 2 year old. They are awesome sleeping bags that you can cinch up with clips while they are small and then expand as they grow.
The best piece of advice I can offer is to bring snacks, something to capture bugs, frogs, and other critters in, and just make the experience as fun as possible. Stay calm regardless of the situation to ensure they are always happy, if you lose your temper out of frustration it creates the opportunity to ruin the trip for the kid, making every future trip more challenging. I'll put in more thought but if you haven't invested in a decent carrying backpack, do so. Both of our kids have loved getting carried on my backs because of the views that transition to naps. When our oldest was young he would sit in the pack for 15-mile trips consistently through the summer before boogying around at alpine lakes.