It can be different for all children. DS1 toilet trained at night at age 4. He was lazy, on a couple of occasions I forgot to put on night nappy, he woke abt 4am telling me he needed his nappy, refuse to use the toilet, then wake at 6am with a very wet nappy. DS2 was 2 yrs old, once the toilet training penny dropped he was day and night trained within days. He would wake, wearing his nappy, refusing to use it and only go on the loo.