A 2 year old should wear diapers if they are not ready to be potty trained.
Or if the 2 year old is still wetting the bed at night or has wetting accidents during nap time then they should wear diapers.
A lot of 2 year olds and even 3 and 4 year olds wear diapers which is okay.
A 2 year old should be potty trained but only if they are actually ready to be potty trained.
Not all 2 year olds are ready to potty train which is normal and okay.
There's no set age that a child has to be potty trained by and be out of diapers.
The child should wear diapers until they are ready to use the toilet.
Although some kids are ready to potty train by 18 months to 2 years of age not all kids are ready by then.
2 years old is actually a bit young and although they may be able to use the toilet the 2 year old has little bladder control.
This means that the 2 year old has to get to the toilet pretty quick before they pee their pants.
So to me at least 2 years old is still a bit young to stop wearing diapers.
If you have to constantly take the 2 year old to the toilet to pee every 10 to 20 minutes and they continue peeing their pants then they are not ready.
I would personally wait until after the child's 3rd birthday to begin potty training as it's easier to potty train a 3 year old than it is to potty train a 2 year old or a child under 3.
Then again some kids are not ready to stop wearing diapers and potty train until around 4 years of age.
All kids are different and will potty train when ready.