This can vary State-to-State and can vary based on the Law Enforcement's jurisdiction, but generally you will have five (5) days to fix the issue if you receive a warning.
The law can hold Leslie liable for multiple reasons. I believe all except "strict liability" are possible. By failing to supervise her children, they chose to do something they would most likely not do with her around--battering Mrs. Timmons' plants. This was an act of laziness, which lead to negligence.