quite a lot goes on in the reported video.
it looks like there is the possibility of foul play unless we were able to view the original bit of footage. Reason I say this is that the video online is a bit jumpy in places and makes analysis difficult. The zoomed in section of what appears to be a child jumping up and dropping down from a tree is especially jumpy. It might be my net connection/pc power.. can't say for sure, but it does leave some doubts in my head.
Looking at the video from a "witness" point of view, then it appears that it could be simply an ordinary scenario.
So, let's play it out...
The young child is running towards a tree that he knows someone is hiding in. You will see an adult move out of camera shot on the far left as the child runs down the path. (possibly the parent(s))
The young child grabs, or has, an item that is thrown up towards another child who is in the tree. As item is moving upwards you can see the possible movement of an arm in the action of throwing something. You can see it move just above the grave stone below the tree.
Then we see the other child drop from the tree along with the object thrown. The child that drops fromthe tree seems to be bigger than the first, but this could be just due to movement speed. (There is an odd moment on the trunk of the tree where I can see what appears to be a leg which seems to be clasping the trunk of the tree. the leg moves twice before you see the child drop from the tree).
The child in the tree cannot be seen until jumping down, so this could be down to a bit of sunlight shining through a gap and directly onto the child.
But then it could be something else