Of course your example would be flagrant trespassing. But the story here is unclear about whether the kids were actually trespassing. What is the definition of that in this jurisdiction--where a body of water is owned by a group entity such as an HOA or a local or national government? As I recall, a coastline within a certain distance from the water can be open to visitors passing through, or even fishing, and I've seen it apply to lakes.
The law is not cited here at all, whether concerning possible trespass, possible violation of gun regs (spit!), or menacing others with a gun without a proper legal justification--such as an alleged intruder who poses an immediate physical threat.
In all likelihood, a common theme in Florida neighborhoods is retention ponds to handle the runoff from summer thunderstorms and potential hurricanes and tropical storms, these neighborhood ponds and lakes are all owned by the HOA which has the responsibility to maintain them, in our neighborhood we have company hired that puts in a small johnboat and motors around spraying the shoreline to keep down weeds that could affect runoff and breeding grounds for snakes.
It’s possible in this neighborhood this is not the case but almost universally HOAs are not going to allow fishing, swimming or boating in the HOA owned bodies of water because of liability reasons.
Nearly every body for freshwater in Florida is likely at some point to have an alligator take up residence, if a kid were attacked by a Gator because they were fishing on the shoreline and the HOA didn’t enforce the rules, they would get sued into oblivion.