Anywhere the child spends a significant amount of time should have their own set. My brother had 4 sets: our house, school, grandma’s house and in my mom’s purse (car/out). A friend had 3: mom’s house, dad’s house and school. As a nanny, I carry a set, they have one at home and school, and if they spend significant amounts of time at another parent’s house or grandparents’ home, they have one there. For occasional trips, especially when I drop off, I leave my set with them.