I'll jump in and echo what others are saying WRT mid-size vs. full size. Unless you drive in the big city a lot and/or have a small garage I can't see much reason to favor a mid size over a half ton. You have two kids, and kids have a funny way of growing. Before long, that "mid sized" truck is going to be absolutely full of people (you didn't mention if you have a dog) and even then, it's not going to be that comfortable.
The cab on my F-150 is absolutely cavernous. Not only that, unlike "mid size" or compact trucks, the crew cab in the F-150/F-250 (and I presume most other half tons as well) has a completely flat deck, IOW no big "transmission hump" taking up space. That makes it very convenient to put groceries or other small items in the cab (with the back seat flipped up) that would otherwise have to go in the bed.
I think the whole "buy an old truck and keep it running" idea is one that looks good on paper (or on the internet) but while it may be more beneficial in terms of actual $$ costs, there are non-monetary costs that you have to factor in, like when your transmission craps the bed in the middle of nowhere and now you have to (a) pay $200 for a tow to the nearest town (b) pay $3600 for a new transmission and (c) extend your vacation by two days and stay in a KOA while they fix the transmission.
And if that sounds oddly specific, there's a reason for that.
(my favorite part of this is the t-shirt I picked out to wear that morning.)
In strict dollar terms, you are still ahead of the game on an old truck vs. a new one, but who wants to put up with that kind of possibility, especially when traveling with a family?
