You might not want to hear it but it is the most practical thing you can do when it comes to living with your adult child.
How much charges will you be having with regards to rent and other things? What can the adult child be able to pay when it comes to charges? If they are living with you, then obviously he will not be able to pay for some rent and other charges.
Ask him why he wants to live at home and what can he do to make up with the expenses of the house? If he is there to study at school then you can take off all the charges and have him focus on studying instead.
You need to ask your adult child how long will he be living with you at home? Some parents do not want to charge for the rent for the fact that he is their child but for some, they need to teach him independence so they need to help him get back on track then start charging the rent.
You need to talk to your adult child about the additional expenses at home now that he is back.
You need to make him understand that these additional charges will go around and benefit him since he will also be taking advantage of the heating system, the electricity, and the food from the grocery.
He needs to know that a family budget is in the works.
If the adult child cannot pay for the rent, then charge him with other things instead.
You can let him pay for the rent by letting him do labor and other house chores instead.
Adult children at home should be able to live independently from their parents.
They should always be able to clean their own room and wash their own clothes.
You can also ask them to do some house chores to pay for the rent like helping clean the backyard or do the lawn.
Ask the adult child if he plans on staying for a longer period of time.
If so, then you need to discuss things further.
Tell him that no matter how many rent charges he has paid, he needs to live by himself in a matter of time so that he can learn to be independent.