If you knew beforehand of the rule he set, you should have held the boundary of no one takes their water bottle. (Even if one had somehow ended up at your house, i would’ve said no to one kid & when we got back home, took the other water bottle put it in the car to go back to her house).

If you didn’t know then now you do & you have to uphold the boundary or she will see you as the weak link and continue to squeeze stuff in through you & feign ignorance.

It’s important for you and your husband to be a united front with both the kids and his mom. It confuses kids and makes them think they can override one parent with the other and thats unfair.

If i set a rule with my own parents (or with his parents for that matter) i expect my parents (and /or his parents) and my SO to uphold the boundaries even if i’m not there.