no the sister really does punch him as hard as she can in the balls during a diaper change and the mom makes fun of the sons pain

It sounds like you’re describing a humorous scene where a sibling rivalry gets taken to an extreme during a diaper change. Sibling interactions often lead to funny (and sometimes chaotic) moments! In this particular scenario, the exaggeration of the sister's punch and the mother's reaction can provide a comedic twist, highlighting the playful yet sometimes rough nature of sibling relationships. If this is part of a story or a script you’re working on, how do you want it to develop further? Do you want to explore the characters' reactions or perhaps the aftermath of the incident?