Hello volsrock,
No, that's not exactly true.
CDC - Causes of Death by Age for 2016
This fake news alternative fact obviously began when somebody used the above statistics and learned that for ages under 15 there are more drowning deaths (828) than gun deaths (461.) The CDC does not cut off statistics at age 18, so there is no way to determine what kills more kids, but the CDC does give a statistic for age group 15-24. When that is included, all drowning deaths (1,420) pale in comparison to gun deaths (7,818.)
It should also be noted that it is a stretch to use the CDC numbers to claim this is from backyard pools. The numbers do not differentiate. It is drowning deaths. That could be from a washtub with an infant, a bathtub, a river, lake or the ocean.
Given the data available I will most definitely disagree that backyard pools kill more kids than guns. Not true. Fake news. Don't fall for it.