No, it’s not “obvious” that the reason is “so the child isn’t being molested”. I’ve baby say many kids in my lifetime, and I have 3 children of my own. I’ve never been asked to do such a thing nor would I ever ask anyone to do such a thing.

If I remotely suspected that someone could molest or harm my children, they certainly wouldn’t be babysitting.

Normal parents don’t ask you to video or take pictures of their child bathing or being changed. They could turn that whole thing back around on him and claim he was creating and distributing child pornography. And the fact they were pissed he didn’t do it is concerning. If they were worried, especially for “safety reasons”, they would have come home, not stayed out a couple hours.