We find the problem with winter living in our camper van is not the weather but the short days. Our VW seems awfully small for just the two of us and we spend a lot of time tucked up in our warm bed reading. It might be a bit hard on a 5 year old. When our two were small we tended to avoid the winter for family camps.
I used to take my two boys backpacking, leaving my wife at home. We all remember the time we were pinned down by a two day blizzard in the Peak District one Easter.
The OP does indicate that some compromise is in order. May I suggest that family life sometimes means having to subordinate personal plans temporarily. I well remember the frustration of not getting out on longer solo treks because of family responsibilities. But circumstances change, kids grow older and and we all adjust. I personally don't think confrontation is the answer. Give and take has worked best for us, but I have to admit to a few rows about personal freedom over the years. Joint decisions mean joint responsibility for success or failure and no one takes the whole blame - or credit!
Mothers worry: it's a fact of life. Our little boys are now 50 and 47. One earns his living flying the world sorting out international problems and the other grafts hard running his one-man business in rural Spain. Do you think she still worries about them? Too damn right she does!