I had a 9-yo mother's helper who rocked my socks off
She was AMAZING though and I mostly stayed in earshot but didn't need to. She was responsible enough to take him outside unsupervised or be left completely alone with him for short periods, but I never let her.
She would ask to come over and play with DS though- I only paid her when I asked her to come over. She would either get 5 bucks or a trip out for ice cream, depending on if we had cash or not.