When should your child stop wearing diapers? As soon as you start potty training, your child should stop wearing diapers. Your child should wear underwear full time and if you're concerned about an accident during a car trip or at night time, then you can put a diaper over the underwear. It's important not to switch back and forth between diapers and underwears because the child can get confused or he may forget which one he's wearing. He may be out and about and say, "Hey, mom, I need to go pee but am I wearing an underwear, am I wearing a diaper?" You don't want that to be the case. You always want to make sure that your child is wearing underwear once you start potty training.
Again, if you're concerned about accidents either in the car trip or on a bus ride or at night time, have your child wear underwear but put a pull up or a diaper over the underwear to prevent accidents. If your child has accidents, you may get frustrated but it's really important to not put your child back in diapers. Once you start potty training, he needs to be wearing underwear full time.