Three brothers from Henan drowned in a village pond. The youngest was under 3 years old. What was the secret?

First of all, the person who fell into the water could not have been actively swimming, but accidentally fell into the pond, because the oldest person who fell into the water was 12 years old, and the two younger ones were only 3 years old. It is impossible to go there at such a young age. People swim in ponds; secondly, since a pond can drown people, it should be protected by guardrails. However, there is only a warning bar on the edge of this pond. The drowning people do not care about children, and some of the children are not literate. The warning bar is in vain. The pond is not a big river, so it can still be enclosed with a fence. I have to say that the official should be responsible for this.