How would disney know if a parent is a single parent?
The ticket part they could see. Still when you made the reservation you could have opted in for the
DDP and the intention was to bring all 4 kids but before tix are bought only 3 kids are going, 4th one want to stay with dad. You could argue that then all you need to do is change the reservation. But if you rented the reservation from a broker then changing it might cost money and you dont want to spend that money so best to leave the reservation alone.