Personal opinion, house chores don't have to have "rewards" you are telling him he is helping you, so like it's your job to clean but he's a good boy for helping you. Nope, house chores are a family duty, not mom's duty, so you don't get a reward. This being said my son does whatever he's able to do. Prepare the table for dinner, brings cutlery, cups and plates to the table, unload the dishwasher and things like this. He needs a reminder and sometimes when he's tired it's hard but we are getting there
My LG helps chop up veg, wash up, load the washing machine, set the table, dust. She doesn't do it for any reward, just to be involved
I think as long as it's not going to hurt them, doing anything is fine. My son helps do everything, loading laundry, dishwasher, pots, bins, cooking, hoovering. I don't think age appropriate is a thing it's more what they are capable of doing individually. Xxxx