did i witness child abuse?

my brother in law and his wife were over at my house with their two kids, a girl age 2 and a baby boy who is 2months.

my son is almost 5 months, so with two boys close in age and a close relationship between my husband and his brother, i feel like we are destined to spend a lot of time together.

now ill just say i dont agree with their parenting choices, but i dont find them to be “bad parents.” their daughter barely speaks. she communicates w grunts because they dont really make her use her words. they guess as to what she wants and just give it to her or they screech and grunt back at her. its not like theres something wrong that she cant talk. ive heard her use mainly defiant words. no, go away etc. so where i would promote language development and asking politely for what we want, they just moan. this is what i mean by parenting choices.

so anyway, the guys are on the nee carpet in my living room with the babies. my sister in law and i are on 2 different sofas nearby. and my niece is whining and grunting. theyd been over about 2 hours at this point and my niece had been making noises the whole time.

but at this particular moment out of frickin nowhere, my brother in law open hand slaps my 2 yr old niece across the face.

i was in such total shock as was my husband. the wife did absolutely nothing.

not that my husband would ever lay a hand on my son, and believe me after this moment we talked a lot about it, but if that were my baby i would be making a scene!

its a few days later and im still having a really hard time with what i saw. i encouraged my husband to have a talk about the right way to handle himself. if not in his parenting, then out of respect for our home and what my son (even though hes just a baby) sees.

its just super inconsistent to allow whining and then slap a baby bc theyre whining and at that moment it annoys you.

i had a moment alone with my mother in law and i mentioned what happened. i told her not to say anything but to look for anything inappropriate. i really dont care if he knows if i said something.

but i now worry about spending time with them. what would you do?