There is no night-time "training."
Night time dryness... is a whole DIFFERENT process, than day time pottying. It has to do with the biological development of the body.
Night time dryness... takes even until 7 years old, and this is normal, and per Pediatricians.
Kids, no matter what age, will still have accidents even if they are potty trained. They are kids. They have accidents.
When my daughter was that age.... and in Preschool, the Teachers said it is NORMAL and that is why parents have to bring extra clothing/undies to keep in their cubby.
Kids in Kindergartenn and 1st grade, have accidents too. NORMAL. This is per our Pediatrician and Teachers I talked to.
Even if just damp wetness on the undies, this happens. Or it can indicate a urinary infection.
Or they can't hold it long enough... even though they 'think' they can. They still don't have complete impulse control at this age nor with their bladders.
And, if distracted or wanting to keep playing, at this age or older, they 'think' they can hold it, but then its too late and their bladder is just too full by then. They won't always say it.
This is common.
Don't scold.
It is about impulse control and the body's cues. And about their nerve/brain/bladder development.
Remember, night-time dryness ALL night... is not attained until even 7 years old. It is their body development, not the child being naughty.
My daughter is 7... and every blue moon, she still wets the bed at night sometimes. Normal. No biggie. I just use waterproof bed-pads under her so the bedding does not get soiled. She gets up, tells me, she washes off real quick, changes PJ's and goes back to bed. No biggie.
My daughter was 5 years old.... when she was able to be 'dry' at night and stop using night-time diapers.
-When she was 3.5 years old... she'd get wet undies too. So did the other kids in her preschool class. The Teacher made no big deal about it nor any drama. It is normal. It was not a problem.
all the best,
Susan