No I don't wash their laundry. If a dck gets pee or poop on their clothes then the parents get a goody bag at pick up time.
Most kids have spare clothes here and I have kept a stash of sprae clothes that my own kids have outgrown just in case so I should never be in that situation.
I don't even wash my own families laundry during peak hydro hours so no way am I running a washer and dryer for someone elses' items.
A few weeks ago I did leave a 'goody' bag here where the DCG had peed on her pants and undies by accident. Since I forgot to give it to the parents and it was going into a weekend I washed it over the weekend (separate from my own family clothes) and returned it to the family but ONLY because it was my forgetfulness and because I didn't want it to get too rancid over the weekend