Potty training tips?!

K

My son is almost 3.5 and mostly non-verbal. He understands the concept of going to the potty. He knows when he has to go. He knows what he has to go. He understands us when we ask him if he has to go. He will even put himself on his potty sometimes (it’s always near him so he sees it). But then there’s the times more often than not when he chooses to go on himself. There has been several times where he’s pooped or peed in his underwear and continues to play until me or my fiancé notice. When we’re cleaning him up and asking him why he didn’t tell us or why he didn’t go when we tried to sit him on his potty before that, he will laugh like it’s the funniest thing. I just can’t figure out how to make him stop. He doesn’t understand sticker charts or rewards, he will want all the stickers at once and throws a fit when I won’t let him.

My family talks crap about why he’s still in pull-ups when I take him out in public. I’m trying so hard and half the times he’s refusing. Please help? Tips? Tricks? Advice?