I can't help but thinking this is a great opportunity for you to help turn three young impressionable lives around.
If it were me, I would defer pressing charges and make these boys a project of mine. Hard work, mixed with man to man talk, some teachable moments, praise when due. Feed then a square meal at lunch, more hard work, etc. Interject some common sense wisdom. Answer their questions about what your plans are for the park - your vision.
My guess, out of the three, only one will respond. But isn't this what it's all about? These aren't hardened criminals. Oh yes, they are well on their way to becoming that way. You have a perfect opportunity to make a difference in their lives. And it looks like you could use the help long term. I think this situation could end up being rewarding for everybody.