No flames please ... just stating my opinion.
There is only one person who I trust with my kids safety ... ME!
Sure, there are calculated risks I take every day in relation to my kids safety and well being, but they are calculated risks. I look at them carefully and decide for myself if I am willing to take that particular risk or not, or do something about the risk itself.
In other words, if there are big kids playing/rough housing in the little kids pool and with my one eye that is always on my kids, I notice that my kids are in some sort of danger (that is a continuous recalculation that goes on in my mind 100% of the time), than I either remove them from that situation or I resolve the situation. I (this is just me though) could get up off my relaxed sunbathing behind and walk up to, and strike up conversation with, the lifeguard/CM and ask him/her if he/she thought that "those kids might a bit too big or a bit too rough to be playing like that right next to my little 3 year old" ... etc.
I know, your expectation is that the CM or lifeguard is going to stop things before they get too out of hand, and most of the time I noticed that they did a pretty good job. But of course, depending on how big or small your child is, or how close to the "rough housing" your kids are, etc. .... remember you are continuously recalculating risk ... you may need to step in before the CM does.
Anyway, in my personal and humble opinion, especially when your kids are very little, this is
always a problem at
any public place where there is a wide range of kids. Kids will be kids .... parents need to be
parents.