I require24 hours (minimum) after light sicknesses, and 48 hr after the sick are well, for things such as the flu and other communicable illness. I have noticed I have some parents that will try and push by 4 or 5 hours...I state very clearly my contract is a minimum of 24 hrs, not as "close as possible" to 24 hours. If they can get an inch from you they will try for a mile every time.
I too, would be uncomfortable with having a Mom come in to feed the baby, does she have a "set" pick up time every day? if, feed the baby even 2 oz before she comes and he will be set for the road home, if she doesn't have a "set" time, ask her to give a quick call or text as she leaves work, so you can have the kids fed and ready to go.....again....give an inch.....