Whether a parent must be present when a juvenile is interrogated by the police depends on two things: The circumstances, and what state you are in. There is no federal law that I am aware of that covers this, and if there is it does not apply to state and local law enforcement.
In some states you might need a parent present if the child requests one. In others, a parent might be required to be notified if a child is a suspect and is to be interrogated. Still, in others, a parent may never have to be notified by the police. It varies by state and by circumstance. In my state we have no such parental notification law ... in others, they do.
For the most part, the only federal standard that applies with regards to the interrogation of juveniles is Miranda. That is if the juvenile is both in custody and being interrogated, he must be read his rights and understand them.