Being dry at night is entirely different then being potty trained at night. The vast majority of the time, it isn't something they can control or learn. Their body has to mature. The body actually produces a hormone to decrease urine production at night, that is what allows most of us not to get up during the night. The production could start at age 1 or age 6. Night wetting in older children is still common. It is not unusual for a child to be day trained at say age 2 and then still in diapers at night at age 4.
Some people swear by the cutting off liquids at dinner time, no drinks before bed, waking them up to go pee. Those things can help, some children. The cutting off of liquids is something that most experts or research doesn't show that really works, the hormone production plays a larger role. Other children are true night wetters, what I mean is that they are just not peeing once a night where waking them up at 11pm is going to help them stay dry at night, these other kids are peeing multiple times a night. Their bodies are not mature enough yet. I do have one of these. She is 6 and has been wearing Good Nights since she was barely 3 years old because she pees SOO much at night, regular diapers or pull-ups will not contain that volume of liquid. We've consulted with various docs (she has several specialists for health conditions) and the theory has always been that due to how much she pees at night, even trying a bed alarm (which are meant for age 6 and up, not for younger children), is not going to be successful. We have to wait until she isn't peeing so many times at night.
Pull ups, even the night time ones don't contain a lot of liquid. Other options could be regular diapers or the night wetting diapers for older children which are Good Nights or UnderJams which are meant for big kids so they hold a lot.