The subject problem sounds manageable without knowing all the details.
Getting a picture of these people fishing does hold weight, but getting something like that through the trouble of the courts may be premature and the law does not have time for a lot of these types of things.
If you have pictures, you then can find out who the kids are and you then have so many more options on how to deal with it. Many times, a simple face to face dialogue can be very effective.
The shooting range option, while usually very effective, will likely be a hollow threat here with being adjacent to a public golf course and other homes.
