Not Knowing What to Do
Before you get enraged at the OP for not doing anything, despite knowing that the children were clearly physically abused, please remember this. Babysitters, or at least those that don’t work with an agency, aren’t armed with the knowledge of how to handle domestic abuse cases.
If that’s not enough to calm your fury, maybe you can relish in the fact that the OP felt miserable for not doing anything, and that fact still haunts them to this very day. We know that they were in a dilemma, and hopefully, they’ve learned how to handle such situations in the future.