I was in San Stef from 7th to 21st June, we hired a boat and headed down toward Paleo, we stopped at a cove and were diving off the boat and I got stung whilst swimming
Not particularly painful just a bit uncomfortable, got some cream from the chemist when we got back and it took it straight down. When I actually looked over the side of the boat there were quite a few of them all about the size of a cup bottom. If you have small children perhaps keep an eye on them on the beach and in the sea, I can imagine it wouldn't be a nice experience for little ones!