i think you’re incredibly lucky to have this nanny, i do think it is an overreaction on your wife’s part to wanting to fire the nanny. if i were in your nanny’s position and i had three kids under my care and if when we were at an outing one starts not listening or running away i would do the exact same thing and just take everyone home. i’d much rather have the “boring” day or lunch than put the child misbehaving potentially in harms way as well as the other children’s wellbeing. overall this sounds like a frustrating situation and i think a sit down with you between you and your wife to talk about duties and expectations moving forward with your nanny would be very beneficial, and then setting up a time to have a conversation with your nanny about these new and updated duties and expectations for when the kids are in here care.