I don't have contract hours but can see the benefits to them. If I was open 10-12 hours than I would seriously think about implementing them. Random drop off's drive me crazy...I am not a drop in centre! I prefer to do the "fun" things when all the children are here and if I have to wait for an hour past their normal drop off time, it does annoy me! However, I don't feel it's fair to the kids to miss out because their parents think it's a come and go. I ask parents to text me if they will be later or earlier and when they start to slip I just put a reminder in my monthly newsletter. I think it would be fair to introduce contract hours as long as you give adequate notice. I would make the late fee steep if it's something you dont' want happening.

As for your PS. I would say, "xx had a great day today. We did blah blah blah. Hope you have a good evening, I gotta run now. See you in the morning!" and I would try to be outside when they came so I could leave to the house while they go to their car.