I had to read you other posts to see where you were coming from. I totally understand how you feel about med/surg and can understand the passion for psych instead of other units.
Get to know the laws in your state regarding holds, etc. In our adolescent psych unit, we are frequently floated over to adult, so find out if the same will be expected of you.
Focus on your interactions with parents, family dynamics, rules (especially regarding phone calls and visits) and how you're a team player. These kids will often try to use staff against each other and it's important, just like parenting, that all staff is on the same page.
Read as much as you can here: American Psychiatric Nurses Association - American Psychiatric Nurses Association