I'm interested in getting a "50's F100.Wondering what year cabs could fit me,my wife and young daughter?(5)

 

I've ridden three across in one of these series cabs for thousands of miles back when. Gets kinda tight after a while. Five daughters, total of five??????? "daughter?(5)" Five across ain't gonna happen.
Get into a sixties or later series crew cab.

 

One five year old.

 

A 48-52 cab is smaller/narrower in comparison to a 53-56 cab. With a stock bench seat you can fit 3 but it does get cozy quick. Keep in mind, even though "by law" you may not need seat belts in an old truck (because they didn't originally come with them) many areas still require little ones to be in a car seat or booster seat regardless. My state requires "the car seat to be properly restrained and secured". Their is no exemption for older vehicles. So you have to accommodate the booster/car seat and have a way (seat belts) to secure said device. As a matter of safety, the kid should always be safe and secure, as I am sure you would agree. Can you make it work, sure, but I would buy a 53 and up cause of the little extra room and plan on adding safety belts and being a tight fit. Just my .02.

 

Just a suggestion. While it isn't exactly the same due to the taper of the cab and interior layout, you can find a bench seat model Ranger or S10 pickup and see what the room looks/feels like. They are common bench seat swaps into the 48-52 models and would give you an idea of the seat width.