*Hearsay* is generally not *admissable* in court. That's not really the question though............
You asked if a minor has to *testify*, which is a different subject. As long as he does not incriminate himself, then he would be required to testify (as racer stated), although many courts would not force someone to testify.
The testimony may be objected to by the opposing counsel because it is hearsay (if it is), which again is generally not admissable.
It is not necessarily hearsay if the testimony is to prove that the minor was told something, as opposed to trying to prove that the "teller" did something.
In other words, the testimony would be similar to being "I heard such-and-such" which is direct testimony, rather than "Billy did this."