My son turned 3 a couple months ago. Around his BD, he had pretty much learned to do all his poop in the potty. He has no problem peeing in the potty when I prompt him to go, but if I don't remind him, he will wet his pants the majority of the time. We have been working on potty training since he was 2.5, so he has plenty of experience using the toilet, he loves to "pee like daddy" (standing up), but he just very rarely actually tells me he needs to go. I find that even if I ask him, he always says no doesn't need to pee, and then he'll have an accident like 10 min later.
In other areas, he is doing all the expected stuff for his age, this is really the only thing that he seems behind in, and I just feel at a loss as to how to help him get the hang of it.
It does frustrate me to be needing to be either going through several pairs of underwear and pants *every* day or to be trying to remind him at the right times to go. But I am trying very hard to be low key about it with him. When he has an accident, we have him put the wet clothes in the washing machine and help with getting new clothes, so he has some responsibility in it, but I try to just remind him- next time let's try to do that in the potty etc.