If assaulted at a house are the parents liable or their renters insurance liable?

More information is needed to properly answer this question.  For example, you mention parents. This implies the assault was committed by a child. Parents may or may not be responsible for a child's conduct. It depends on various factors such as the age of the child, what the parents knew about the particular situation, etc. Generally renter's insurance does not cover intentional acts so it is doubtfull there would be coverage.