New to BYC, and jumping in full boat!
Welcome! Sounds like you are well on your way into the adventure, it is wonderful that your whole family is getting in on the excitement. What breed(s) do you have and have you ordered?
Always better to go big in coops, runs etc. When you "build it," they will come and fill it up. Then more and more. Better to be large than adding more coops down the road.
We are all enablers here, so we will never say you have too many chickens.
Welcome to the obsession. You sound like I did last year. It was my family asking to get chickens and it was I who begrudgingly relented. Now I'm completely wrapped up in it.
I agree with the post above. Build bigger than you think you'll need. Assuming you have full size chickens and not bantams, you'll need a minimum of 48 sq ft in the coop and it would be good to have a run of at least 120sq ft. This site is full of great information. Have fun.