How much rent to charge adult DC?

[Lentilcakes]

Both DC will be living at home from the start of July.
One works part time in a nice retail job / trying to launch career.
One will have finished uni and is applying for jobs. He has a lot of savings as he worked for a year prior to uni. He has a big appetite cos he’s a tall lad - eats about two times my food consumption. When he’s home the food bill skyrockets.
DD will buy ‘extra’ food for herself as she’s not always keen on my meals as we have very different tastes in food. DS will eat my dinners as he likes me cooking.
I agreed w DH that we’d charge nominal rent of £50pcm each as we do want them to save, but I think as adults they need to contribute to the household. Obviously they clear up after themselves, do laundry, keep their rooms and shower room clean etc - that goes without saying. If they start working f/t then we will increase the rent.
Does sound fair (they’re 22 and nearly 24)?

20yo (working FT, didn't go to uni) pays £100pcm as a contribution to the utilities, plus buys his own food and cooks for himself.

I do most of the household laundry, including his.

I have four. I did charge my eldest a little amount but only really because his gf lived with us too and I didn't think it right that she didn't pay anything so charged them both !
DS2 has just bought his own place. I didn't charge him anything because he has not gone to Uni like the other three have, so has cost us nothing in that respect. Living rent free has enabled him to save and buy his own place.
Ds3 has just graduated and as with many new graduates is yet to find a decent full time job but has just started a part time retail job this week. We won't charge him because he will be earning a small amount. Also he is barely at home and spends at least 3 or 4 nights a week at his gf's home. Maybe gf's parents should charge him ! He also barely eats anything except main meals when he is here.
DD4 is at Uni. I doubt I'll charge her anything when she comes home next years.
At the end of the day, the mortgage is paid off, we would still be paying the same council tax whether they live with us or not, so it's just the cost of food and one quick shower a day that is extra. If I was a lone parent with rent to pay things would be different.

My DDs first take home pay was about £1600 per month. We charged her 400 a month which included room, bills, food. We also still paid for her if we ate out or got a takeaway.

I lived at home after graduation while I was struggling to establish myself in my career, and I’m very grateful my parents never asked me for rent. I contributed to the household by cooking, cleaning, and occasional buying groceries.

I don’t charge mine as they are saving for deposits on houses. I can afford not to charge them though.

I'm very much in the "adults pay their own way" camp (once they're done with uni, where we supported them), so I charge mine £200 per month, I think it ought to be nearer £250 for their share of the bills though.