I have a month's notice for the same reasons as you gave. I would give the notice now with the idea that if things turn around totally in two weeks you will revisit but if not the termination stays in effect. I would leave it at that and say nothing about the deposit at this time - many parents almost forget they did that. That way they are more likely to just pay for the current two weeks and then you can remind them that the termination will stay in effect and oh by the way I will use your two week deposit towards those weeks.

If you just want him gone then give notice and let them know they can leave anytime without giving additional notice and use the 2 week deposit and hopefully they find care before the month is up and leave early on their own.