I think its a foreign short film in French or Spanish (74% sure).  A social worker or teacher (woman) is worried a about a young boy. One day she visits his home carrying a box (cake box maybe). She comes into the apartment, then the boy and his father restrain her ,then start chopping her up bit by bit.  the woman is trying to tell the kid something.  the kid notices she is gesturing toward box she brought with her.  the kid goes to the box and opens it–it a birthday cake with a bloody cat head on it.  The kid is like dad wait (non verbally).   not animated film