Is it illegal for (2 year)old children to throw something in to a neighbors yard?

I have had this nasty neigbor move in recently. She is so unfriendly and rude!! I have three kids who are 2, 4 and 9. My smallest one recently threw a few lemons in her yard and she was LIVID! If she calls the cops, can I get in trouble. My son get in trouble when he does it but he hasn't caught on yet. I'm scared he's going to do it again (of course when I'm not looking) and she will report us. Can anything happen?