I have a pretty high tolerance for other children being unruly, but there comes a time when enough is enough and in certain situations I will say something. This particularly incident I doubt I would have said anything such as the OP, but I wouldn't have a problem with her saying something if I were in the hot tub as well. I'd also have tossed in the 'I heard it too' if OP decided to say something. Say something myself? Eh, this one isn't really on my radar. The incident needs to be a bit more extreme for me.
There were 2 young children running around like banshees in Cape May during our dinner on the last trip. Absolutely insane. Yelling, screaming, throwing themselves on the floor, touching tables... and the parents sitting next to us - you'd think they were on a date solo. They paid no mind at all. After touching our table, bumping into me, screaming loudly for a good 30 minutes, and eventually taking a french fry off my daughter's plate, I finally looked at the mother and said 'can you please keep your kids from touching our things.' She just looked at me, sipped her wine, and turned up her nose. Alright then. Mr. McGrabby Hands came back and try AGAIN to take something off one of our plates, but instead knocked over my drink. Enough. I finally just sternly said to the child 'NO. Please keep your hands off of our table and do not touch our food.' He just looked at me shocked and carried on with his piss poor behavior. Didn't come back to our table though.
I'm sorry - but your lack of respect for others around you is a ridiculous reason for me to have a meal, or any situation really, ruined. I wouldn't have a problem with someone saying something similar to one of my kids, however, you'd never have to I'm around because it won't be tolerated FROM ME. If someone felt the need to approach me after I spoke to their child then you are more then welcome - you'll come out of that one looking far worse than I will. I can assure you. If it gets to the point that I've had to resort to saying something you can bet that that child has disrupted everyone in the immediate vicinity and they'll speak up. It takes one person to say something and others will back them up.