Ok you might think I am crazy . My son is eight years old of course I give him the responsible of maintain clean bedroom. Every so often I would clean it. You would be surprise what I find. The main reason is really keep abreast what goes on his room from removing old clothes or finding food wrappers when he is not suppose to be eating in his room.
They clean their room and put away toys downstairs every night before bed. ( putting away toys etc ). I vacuum/ dust as needed and do a deep clean every few months ( to where I'm getting rid of broken or missing pieces etc ) to make room for new stuff.
We do it together since I want to make sure nothing is hiding in shadows like you have found . We have found bowls and cups with residue in them. She was allowed to have a snack, just never put the dishes away.
DD is 5. I do not clean her room. I supervise the cleaning of it, but I do not clean it. I go through her clothes as they get washed/put away and when the seasons change, we go through her toys together a few times a year, and I will sweep/mop while she's at school. But the actual cleaning is left to her.
I help her. She is 6 and capable of doing it herself, but I have found if I go in and pick up a few things with her it gets done with less complaining. I really don't do that much. Sometimes I do it while she is at school, but that is mostly if I am trying to get rid of junk.
ds is 5 and he has to "clean" his room... pick stuff up off the floor, laundry in the laundry basket... that kind of stuff... but i need to get in there to organize... im being lazy cause i meant to do it pre-holiday but was in my first trimester and now i figure i'll just wait to see what the gender of the baby is... THEN i'll have a lot of "nesting" to do hahaha