What Prof says...
Take clothes which can be layered, eg leggings/tights then trousers, vest t-shirt long sleeved t-shirt jumper. (remember, if it's cold and you want them to look good, the bottom layers can be filthy and the top one clean.)
When on campsite just let the DC's wear dirty clothes, if you head to civilisation get changed then!
Take loads of socks for small people. If it's too cold for bare feet you can guarantee they will keep walking on the grass without putting their shoes on.
If baby is very baby then s/he won't need much different than at home, maybe a couple of extra jumpers/blankets. If crawling you'll need a few more changes than usual.
This is what I do for bedtime:
Baby: Vest (long sleeved if possible) and socks, then babygro, fleecy onsie type thing, then grobag/baby sleeping bag. Then I put on a couple of blankets if it's needed when I go to bed. (I put my fingers down baby's back inside clothes to feel temperature, hands are always cold.)
Older kids: vest and socks, winter PJs (long sleeved and legged, warmest they own, but just normal ones.) then sleeping bag. I then have jogging bottoms and sweatshirt/non-zipped fleece jumper for them so they can put that on if cold, or use as a dressing gown in the morning. (can also be used as spare day clothes!) and a blanket.
For grown-ups. just your normal amount of clothes but make sure they can mix and match and be worn layered if necessary, and a couple of extra jumpers. Bedtime: I do the same as the older kids at bedtime (but I'll be wearing extra clothes all night). DH wears boxers and t-shirt as usual, (his sleeping bag must be warmer than mine!)
We take coats into bedroom at night so they can thrown on easily if nightime toilet trip is needed, also if you are cold then can be spread over bedding.