I also suggest including an indirect supervision clause to your contract. State in there that periodically during the day there may be short periods of time in which the child will be left unsupervised (ex. including but not limited to when you go to the washroom, attend to a child's needs in another room, getting supplies from another room/floor of the home). Say that during those times you will ensure the child is safe (all baby gates closed etc). This will cover you in the future.
Thank you mickyc! I have now added this. *few* Live and learn eh?