Tampering/stealing mail, what can be done?

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I took a short day trip today and came home after dark only to find 2 pieces of my mail on the ground, one envelope was torn almost in 2, and one intact package. I know there was at least one other envelope because the torn one always comes with another one like it. I only have guesses to who might have done it, as I've had to chase several neighborhood children from riding their bikes in my front yard (clear up to my porch with no regard). Other than that I have no idea though. Have you ever had anything like this happen? What would/did you do?