What a terrible tragedy and devastating loss. My thoughts and prayers are with the family.
I hesitate to share the rest of this here, but it is so important that I feel compelled to do so. This is not meant as a criticism in any way, but rather as a caution to all parents and grandparents.
I once witnessed the near drowning of a 5 year old girl in our neighborhood pool. She had followed her big sister in but hadn't taken the time to put on her "water wings". She was 1 to 2 feet away from the steps and there were lots of kids around her. The adults (me included) were busy getting settled with our towels, coolers, chairs, etc. Fortunately we noticed in time: I immediately recognized that she was in trouble and was able to pull her out safely. She made no noise and no gestures to call attention to herself.
It can take less than a minute for a child to drown. It happens silently with very little arm waving. Learn what a drowning really looks like (there are numerous videos on youtube) and watch your children constantly while they are in the water, especially those who don't know how to tread water!