K.H.
Hi K.,
Have you ruled out illness? Sometimes pee accidents are just that due to a UTI or yeast rash/infection.
Assuming that's all good to go, is he having issues with the other end? Are the poops all going where they're supposed to at the correct frequency? If he's holding this in it might affect the control of the other.
Does he go to preschool? Have you talked to his teachers? Ask if there was any type of altercations or weirdness at school. Maybe something is bothering him. Maybe there's someone at school that has accidents and he's trying to work out something he witnessed along these lines. You never know.
After those ideas, I'd just ask him if he thinks he needs a diaper again for night time. See what he says and let him decide. This way he still has control of this part of his body. Then in about a week, if it even goes that long, ask him how it's going and if he's ready to get rid of the diaper. Just make sure it's him making the decision to not have accidents anymore. It's hard to not worry, and a pain in the butt to deal with messes, but in the end it's up to him.
If it gets worse instead of better, consider asking your ped. dr. about it.
Good Luck,
K.