While we do not have the full facts yet, I think that at first sight this case is a very serious case. If it is true that the lifeguards failed to check the pool then rather than the sack I think that jail might be the right place for them. I think that a rescue worker who is too lazy to do their job and they are aware that an possible deadly accident is in progress then criminal charges (manslaughter) should be strongly considered.
I would not try to jail the lifeguard if the boy had been unable to speak the same langauge is the lifeguard. If for arguement’s sake a Czech boy who does not speak english was on holiday in the US, and he had tried (and failed) to explain to the pool lifeguard that a woman was drowning then I would write it off as a horrible accident where no one has acted in a criminal way.
My view is a professional lifeguard would is about to go and eat a cream cake or phone someone on his break would postpone the cake or the phone call to allow him/her to check the pool for drowning people.