under WA state law is there a minimum amount of time an attorney has to practice before taking a juvenile dependency case

A lawyer is considered competent to handle a case when he is admitted to the bar. Hence the short answer is no there is no minimum time or amount of practice one can or should have before handling a case.

That said, there is a rule of ethics that says a lawyer should not andle a case he is not prepared to handle. Most young lawyers will take on mentors, either with in a community or a law firm. Some law schools try to partner their recent grads with more experienced attorneys who have worked on cases like the one before them now. State bar associations and locals do the same thing.

Just because a lawyer is new doesn't have the wherewithal to handle the matter. He will likely work very hard preparing and may even find a new take on an old law. OTOH experience is a sure way to know the person you are dealing with is good.

I can only tell you to question the attorney carefully and be sure you issues are adressed.

Good Luck