How sturdy is a 15 week old fetus??

My daughter is super hyper and it's been a chore to keep her away from jumping on or kicking my belly these last few weeks. She has been getting better about being mindful and i letMy guard down and was lying on the couch. She took a running start to join me and leapt forward and accidentally hit me full force (of a 5yo) in the low belly/pelvic area with her little fist. How protected are our little ones in there? It was a pretty good punch but didn't have me doubled over or anything. She's only like 42 lbs.