That is wild, I have not encountered that before. I am a single Mom who no longer receives any child support and my wage was just cut back three hundred a month due to govt cutbacks.....BUT......when my son wanted a sleepover b-day party, he was allowed to invite 3 kids, cause that was what i could budget pizza, movies, and snacks for.
He does have one friend whose family is very wealthy, and when the father drops his son off (which is quite often as he loves being at our home especially since his Mom died) he often tucks a twenty of fifty in my pocket and tells my to take the kids out for dinner or treat myself to something. I do not expect this or ask for it, but know that the father realizes and appreciates that his son is at our house alot, more than my son goes to their house.
In general, my son and his friends give and take, no one gets asked to pay to stay.