Oh my gosh. I could not have stopped myself from taking the book and telling him I thought it inappropriate if I saw that.

I agree that there are times when a parent has been pushed to the limit and is rougher with their child than usual. You can usually tell that it's not an ongoing, normal thing. But this? To calmly and repeatedly beat babies on the head with a book and drag them around when they understandably scream and cry? Child abuse imo.

In situations like this, I think it needs to be stopped. Those babies can't stand up for themselves, their father is beating them and seems to think it's ok and normal. The mother apparently does nothing about it. If someone doesn't stand up for them, who will? Just because it's other people's right to parent how they like and they're not all as gentle as me, I think this goes way too far and I could not just dismiss it as "His child, his right to discipline (beat) how he sees fit".

Sure, maybe you don't want to have a fit right there and it's probably not a good idea to have a go at him, but stopping it calmly and letting him know it's not on might have worked, and I think you're right in going to someone within the congregation for help for them. Maybe he just needs to be shown that there are other ways? And that it's perfectly normal for a child not to stay exactly on a rug at that age? Maybe his expectations of them are to high.