Is it possible to pull bark off a tree with your finger nails?
If further detail is wanted, the child is most likely using all of his strength in attempting to get a hold of the tree to stop the abduction and get free, with little regard to any injury happening to his fingers and hand. The tree in question is most likely pine or a similar conifer, due to setting. The child is about five or six, lanky in build. There was a massive rain storm preceding this scene, so the tree was likely wet.
I know everything I've just typed sounds shady as hell, but I'm honestly just a writer. I couldn't find anything when I tried googling.