A lot is happening in this world, and this is one of the awkward things we would see in this life. It is certainly unpleasant that parents would demand rent from their children living with them, not even bill payment as an obligation. But it's fair if the child could help the situation of the parents if they have retired or are not so rich.

Many children will do this even without asking them just to support the parents. And if the children didn't think towards that direction, parents can still put it to them, but not making it a mandatory periodical payment.