School age care can be hard to find in some areas so I would consider that in your timing since parents will feel they had the school year covered when they signed on with you. For sure it is ok to tell parents now that you will not be taking school age as of the end of June and encouraging them to check out summer camps etc. (which they will need to start doing now).

Many of us only do care for those not in school mostly because of the lost income from school age kids plus the transportation.