I am less concerned about actual damage from taking a bath with a daycare baby than the very clear evidence that the care providers do not have appropriate boundaries.
Bathing WITH a daycare child??? I didn't realize that when you said bathing. I thought you meant she gave the baby a bath. No... no no. I didn't see where you live, but I can nearly PROMISE you that licensing would be completely flipped out about sharing a tub with a child.
Not to mention smoking a joint while in the tub with a toddler. OH, PAH-LEAZE please, please look for other care. I don't care if the most important doctor in the entire world brings their kids there. I bet they don't know about the baths.
I don't think this is sexual abuse at all. I bet it's innocent. Sexual abuse hasn't even crossed my mind. But, this is a bad idea. They are crossing boundaries and making poor choices while your kids are there.
Maybe nothing will ever happen. Or maybe nothing will ever happen while your kids are there. But, why even take a chance? Why risk having the police come in and arrest them in front if your kids?
I said before, the bumps and bruises are part of childhood. The backyard sound amazing. I don't think kids should be hovered over either. I like that the kids can go in and out without being followed around. I notice that my daycare kids play much more freely when they think I can't see or hear them. They enjoy play more if they think I am inside. But, that doesn't mean I'm not watching them. I'm just not always in sight of them. I can ALWAYS hear them, and usually see them. I assume your provider is doing the same. I love that.
But, pot smoking and bathing are not ever ok. Especially if there are 13 other kids running around the center. One teacher shouldn't be in a bathtub with just one child while the other teachers are left to manage the group.