Per our Pediatrician... night time dryness... is not something biologically attained until even 7 years old, and is normal.
My daughter was potty trained from 2 years old. For daytime.
But at night, my daughter, was already 5 years old, and wearing a night time diaper to bed still. She was not dry at night. Then one day, she told us she is fine and wants to wear underwear to bed. So we did. She was fine... but keep in mind, that night time accidents still do occur. That is childhood.
My daughter is 8 now... and just the other night, she had a little pee accident. She sleeps deeply... and once she even had a dream that she WAS on the toilet... until she felt herself wet.
I have waterproof bed pads under my kids... so clean up is way easy. I just replace the bed pad with another one, if they have an accident. No biggie.
We have never woken up our kids at night just to go pee, and have never restricted liquids at night.... just to keep them dry. You figure, a child sleeps at least 10+ hours at night.... and that is a long time... for them to not pee. Even for an adult....
It is hard to make a child, not pee at night... when they are sleeping.... because the flow of pee is not conscious, or involuntary.... when they are sleeping. Until they are older... they will then be able to, biologically and with their body... to awake... when their bladder is full.
My Husband, as a child, was older and still had accidents at night.
all the best,
Susan