Regression

So my boyfriend has a four year old and we've been having trouble with him wetting the bed which is completely normal especially for him being so young he's done extremely well. and we've had a couple accidents with him going poop in his pants. But is it now too early for him to start regressing back to not being potty trained now it's almost as he refuses to go poop on the toilet I told him not five minutes ago that if he had an accident that he should tell somebody so we could clean it up and then he intentionally poops in his pants. I'm at los what to do or how to punish him for this but my boyfriend takes all this extremely serious because he had trouble potty training when he was young