Regardless if it was an adult or child it was a childish thing to do.
My experience tells me it would do no good to report it. We live adjacent to the forest and have reported many issues. The ONLY time they did anything is when my wife went in the ranger station to report freshly dumped bags of trash, including dirty diapers and WIC ID. She waited at the counter until someone got off their duff and did something.
Personally when I found a tree blasted down by shotgun blasts I blamed a recent episode of Myth Busters. Then I picked up 140 empty shotgun hulls and recycled them. Yup- they spent over $40 in ammo to take down 1 tree. Childish? Yes. Adult? Probably.