I would tell the mom that I need to know by July 1st, what her intentions are..so that you have time to fill her spot. And if you fill the spot with a new child, then it works out perfectly that you are losing two next fall when these kids want to return. I wouldn't stress about kids leaving over a year from now...it's a long time away....and we know they can only stay full time with us for about 3 years...