My ds is 3.5 and still has a nappy at night. I have bought the pull up type and told him that he has to pull this type of nappy down and wee in the toilet before bed, in the morning, etc He does this, but his nappy is still soaked in the morning. I limit his drinks in the afternoon but he does have a cup of milk before bed
He is obviously not ready to abandon the nappy yet, but was just curious about your dc,s ages.