Hi Lexie,
I have a 5 year-old that not only wets during the night, but the daytime as well
. So, it could always be worse.
. Boys do tend to wet the bed longer and 4 is not THAT old. If it were me, I think I'd focus on reassuring him that he is 'normal' and that it is not that big a deal. If he can relax about it, maybe that will help.