My husband is generally the one doing the kids' bath (3 yo boy, 1.5 yo girl). Since they started taking their bath together a few months ago, our son started "helping papa" washing his little sister. I personally think this isn't a thing to encourage (on the verge of inappropriate). It would be ok if she was a baby but she isn't that small anymore.
He's just turned 3 so we haven't talked much about his body etc yet, but that something we will do more in the next year or so.
Am I overthinking this? I think I hurt my husband feelings a little bit as he was seeing this as a bonding thing between them.