To get your three year old boy out of diapers you should get a potty chair and then teach the 3 year old boy to pee and poop sitting down.
Remove the diapers and only put him in underwear.
Then when you notice he's about to pee or poop take him to the potty chair and sit him on it until he pees or poops.
However if he has an accident and pees or poops his pants just clean it up and tell him it's okay and that he will do better next time.
Give him praise and have him pick out big boy underwear and make him feel like he's in charge of the situation.
Still if the 3 year old boy is not ready then just keep him in diaper and try again later.
It's normal for 3 year olds to wear diapers and not be potty trained.
Start changing your child's diaper in the bathroom, and suggest incremental tasks such as pulling down pants, tearing off toilet paper and flushing.
When he does finally give it a shot, show him you're happy and excited, even if he doesn't pee or poop.
The average age for potty training and for when a child stops wearing diapers in the day is between 2 years to 3 years of age.
However some children don't potty train until as late as 4 to 5 years old in rare cases.
I believe that you should not force a child to potty train and instead the child will potty train themselves whether it be at age 2, 3, 4 or even 5 years old.
Although most kids are ready to potty train by age 3 to 4 years old some just take longer and they should wear diapers until they no longer need them.
A child should be out of diapers at night once the child has become dry at night.
Daytime potty training typically occurs by age 2 to 4 years old in which the child no longer needs diapers in the daytime.
But nighttime wetting is different and although the child may be nighttime potty trained the child may still have bed wetting accidents.
Bed Wetting is different in that the child has no control over their bladder at night and won't wake to go pee and so they will pee the bed.
So until the child is dry they should wear a diaper at night so that the bed and their clothes stay dry.
Bed Wetting sometimes stops by age 5 to 8 years old while some kids may continue wetting the bed until they are 17 or even into adulthood.
Bed Wetting in children is normal and there's not much that can be done to stop it.
So diapers or pull ups are a good idea for the bed wetting child to keep them dry and keep the sheets and bed dry as well.