Rough 3 year old

Destiny

I’m currently 25 weeks with baby #2. My three year old boy is constantly climbing and horseplaying around, which is understandable. He does know and somewhat understands that he can’t be that way around my belly. But when he doesn’t get his way or gets too excited all the teaching and easiness goes out the window. I was wondering if any other moms had this problem and how to help the problem.