Tenant Problems Food Fighting

[Steven Clark]

New landlord hear so need so advice on the best way possible to handle this problem.

Currently living in a 3 family owner occupied home. Went home for lunch from work today. When I left to go back my car had bread, hard boil egg and I noticed the house had jelly coming out one of the windows. I called my tenant who has an 11 year old that I have caught ripping bushes out before and said hey I noticed there jelly coming out your window.... ect. Im not saying your childed did this however I think its very weird that all this happened and its go to stop. Tenant swears it wasn't her childed but will clean up the jelly. She thinks its one of the neighboring kids. 

How should I handle these issues in the future? What should be done to prevent them from keep happening? Ive only owned the place for 3 months.