I do think it is fine for a parent to do that. Everything is expensive nowadays, it could help the children to understand the meaning of responsibility and how to be independent. In fact, as children it won't matter to pay the rent to your parent as you also helping them lift some burden a bit from your parents shoulder since everything is expensive nowadays. We gotta be realistic about what are we gonna face in the future and help our parents a bit because we will also be a parent one day and not every parents are rich.