I agree with Wonderwiper. I think they chickened out of committing to a daycare that far ahead.

Maybe they had a discussion behind closed doors and mom brought up that she would like to stay home with the baby or she is thinking of a career change and doesn't want to commit the deposit and say 100% that they are going ahead with you because they don't know anything for sure.

It sounds like they like you and they aren't actually saying 'no' to you but they want to keep their options open at this point.

Maybe someone told them they were crazy to sign on for daycare that far ahead? you just never know what goes on behind the scenes.

I do feel bad for you that you spent so much time on them though.

Personally, I would not call them back or email them or ask for a reason because you don't want to seem desperate or chasing after them for their business. I would think it was their loss and move on. I probably wouldn't even sign them if they contacted me back next summer and said they wanted to go ahead because it seems like they are yanking your chain and didn't follow through on what they said they would do. Sure they have a reason for it but it would be a red flag for me.