It all depends on the child as to when the child will be able to sleep through the night without wetting.
Some children become dry and don't need a diaper anymore at night after age 4 and some kids have a bed wetting problem that can last from age 4 to age 8 and some people aren't dry and don't stop wetting the bed until as late as 15 or 16.
In rare cases some people will wet the bed as an adult for the rest of their lives.
In my case I wet the bed until I was 12 years old and I wore diapers for the bed wetting even though at first I refused but I'm glad I decided to wear the diapers because the diapers made it much more comfortable than waking up in a cold wet bed.
Your child's doctor can also prescribe some medicine that's supposed to help slow down the production of urine at night and also be sure to have your child urinate at least a few minutes before getting into bed so they can have an empty bladder.
I did that myself even though I still wet the bed but having an empty bladder helps anyway so you have less urine that will get out at night.