I have 4 children, 32, 21, 19 and 17, and I've always charged them 1/4 of their wages for rent, made them save 1/4 and then they have half for spending.
2 older sons have moved out but I still have my daughter and youngest son at home. They are responsible for their own rooms, washing, cooking and making sure everything is clean after cooking. If I'm cooking a meal I will plate some up for them or leave leftovers on the fridge for them to heat up if they want it. Same with washing too, if I'm doing some washing and I don't have a full load I will offer to do some of their washing. I still buy them toiletries, food and things they need urgently.
Daughter, 19, earns £1200 a month so gives me £300, saves £300 and has £600 to spend. Son, 17, earns £900 so gives me £225, saves £225 and has £450 to spend.
I started charging this pretty much as soon as they got jobs for the youngest 3 and the eldest had his first child when he was only 16, got pregnant at 15, so I took 1/4 off of him as soon as he got a job at 15 to put into savings, didn't charge rent as he needed the money to spend on his girlfriend and child, and then took another 1/4 off of him for rent when he turned 18.
But because I am charging rent I am also relaxed on the rules, they all obviously had to respect me and my home, but I don't give them curfews or rules to follow anymore and they can have friends or boy/girlfriends over whenever they want as long as friends are respectful too and if the friends are expecting dinner when I am cooking they are to let me know.