Past that period of my life now - but, when adult children, for any reason came back to live with me, I always made them pay towards the costs of doing so.
When my 18 year old daughter decided to take gap year before uni, and worked I took a small percentage of her earnings. 50% of this I saved and gave her that money just before she did go up to Uni. Another daughter came back to live with me when she was 20 years old, unemployed and sick. Much to her (then fury) I insisted she gave me half of the benefit money she received each week. Again, I saved all this - and when she finally sorted herself out and moved out gave her this as a lump sum.
Now, many years later she tells me that at the time she thought I was the most uncaring mother possible taking that money - but now she realises how right I was to do that and how it helped her to understand the real meaning of money. She has never been in debt in her life (except, obviously for mortgage), and she puts that down to that experience.
Do not think it is really kind, in the long run, to 'keep' adult children. Part of good education for life is learning how to cope with household bills,, etc.
If you have the room no reason not to have them stay for a limited period. No reason for you to do the cooking and washing. When my son moved back with me when he broke up with his partner, he lived in the house, gave me some money each month, but lived independently -doing his own cooking and washing, etc. etc. He stayed for sometime and eventually his new fiancee moved in with him - I liked the fact that the large house did not have just me rattling around in it. But no way would I have wanted to be a housekeeper/cook, etc for them
