Situational ethics are called for when deciding what to do about hotel rules and other guests.
On a recent vacation, I stayed in a nice hotel with an indoor pool and took my young daughter swimming. The signs around the pool clearly stated that children were to be accompanied by an adult and that no food or drink was allowed in the pool area. There was a group of kids there by themselves causing a huge ruckus, and also an older couple who brought glasses of wine into the water. I said something to the kids about being careful near my daughter but I didn't say anything to the older couple. If I was going to put myself in the role of enforcer, should I have said something to all of the offenders? Was there a better option than getting myself involved?
The hotel management has put up signs to ensure that if someone gets hurt, the hotel won't be the one to be sued. Beyond that, as long as the guests are happy, they probably don't really care that much about what happens on the pool deck. But you, the guest, weren't happy! You could have called or walked down to the front desk to complain. The management may have kicked the offenders out of the pool area. They may have given you some free cookies. They weren't going to keep an employee there to enforce the rules, so the enforcement may have fallen back on you anyway. and it would have been an annoying errand down to the front desk in your bathing suit.
My guess is that the rowdy kids were a lot more disruptive to you and your child than the drinking adults. While kids will be kids, an older couple should know better than to flout clearly posted regulations. The real offender in the case of the kids was their parent or guardian who never should have allowed them to be there unsupervised, so it wouldn't have done you any good to reprimand the kids for being there. Rather, as it sounds like you did, it made sense to help the kids see the importance of acting in a way that was conducive to you and your daughter's safety.
You weren't reprimanding for the sake of being right or enforcing arbitrary regulations; you were looking out for your family. Had you said something to the older couple, it actually would have weakened your position with the kids because it would have seemed like you just wanted to be a stickler for the rules posted on the wall. I will say, though, that the idea of breakable glass near bare feet makes me pretty nervous; had it just been the older couple, I actually might have said something.
You were there to be on vacation, not to maintain any standards for the hotel's benefit. It was well within your rights as a guest to talk to the kids, but you don't owe anyone consistency in this situation. Even if you had an awkward encounter with the offenders at the waffle station the next morning, ultimately, you were all returning to your respective homes, never to see each other again. Your stance only needed to be as strong as necessary to get through your swim session.