I think you have made a wonderful choice!!!! I work pediatrics and am super happy I didn't venture off to med/surg first. Most importantly your hospital should offer some time of orientation/preceptorship that will help guide you in developing your skills and so on. Take every opportunity to DO and LEARN! Don't be afraid to get in there because they are children/newborns, because guess what....that is all you will be getting!!! lol.
I have floated to NICU, and have learned its not exactly my cup of tea. However, there is much to learn there as well. Its not just you and your patient, however, the parents of that family. BE READY for that one! Sometimes parents can be quite...umm...whats the word...'PARENTS' and you may be ready for them to go home so you can work(in NICU and Pedi) but unfortunately they usually are planted right by your side! Learn patience and understanding and at the same time some degree of firmness and voice.
Most of all in either, ASK FOR HELP if you need it. You have picked a great specialty whether NICU or Pedi. Hopefully I answered your question some!
Good Luck Friend