My husbands brother lives with us (whole other thread, don't even get me started on that....) and he's a lazy bastard where anything housework related is involved. Will do what he can to get out of doing it. I was in the kitchen earlier today prepping the dinner when 7yo DD came in dragging BILs laundry bag and she started to pull his dirty clothes out and put them in the washing machine. I told her to stop and she goes "But uncle X likes me to do it!" (Yeah I'm sure he does
) and I said that she shouldn't be doing it as I don't like her handling adults dirty underwear etc. A second later BIL walks into the kitchen and takes over from her and loads it all into the machine.
For context I don't let her do mine and DHs washing either, I know what bodily fluids end up in our underwear
and I don't want her touching it, let alone BILs. She does hers and baby DS' washing quite happily and she knows how to work the machine (she had just turned 5 when she taught BIL how to use it!). I just don't think it's great for a child to be handling adults dirty pants 
I wasn't unreasonable was I?