Well, before making any decisions, I would maybe interview family #2, since they might not even be a fit anyways.
Is dck#1 planning on staying during mat leave?
I'm in the same position as you sort of. I have to make a decision to keep a boy who is temporary with the potential to be permanent or to take on a little girl with better hours in September.
This is the part of running a daycare I don't like...decisions, decisions.

Good luck with what ever you decide!