Familiarize yourself with normal VS for each age (I carried a cue card for the first 8 months in case I was unsure), developmental miletones, and differences in pediatric anatomy (ie airway). Learn all about the common conditions the kids on your ward will have. Whether it's neuro, respiratory, cardiac, or medical, you can bet it will be pretty different from the conditions adults would face on a similar unit.
Become aware that compensatory mechanisms in children often differ from that of adults. With hypovolemic children for instance, we tend to see changes in their heart rate long before changes in blood pressure (in nursing school we learn about shock from an adult perspective). If children are going sour they tend to enter respiratory distress before facing cardiac involvement. This is critical though because they can quickly progress to respiratory arrest then cardiac arrest. Children can quietly continue along until they finally crash - learn what the early signs are to avoid an emergency.
Learn about startegies to assess and perform interventions on children of all different ages (hint: you can't usually reason with the little guys). This will help you immensely in your practice! Try to keep current on popular TV shows and bands. Ask them questions about the things they love and it can help them open up to you.
Pediatric nursing is all about caring for not only the child but the whole family. That child needs the family for comfort and support, the family needs you to for teaching and support, and you will learn so much about that child from the family. Sometimes we are so busy taking care of the kid it is hard being a nurse to the family, especially if they are a challenging/demanding one. Try to give them a time frame where you can talk to them ("I'm just about to start giving out morning medications to my patients. How about in a half hour or so I will come back and we can discuss some of your questions in more detail?"). Give realistic time frames though or you might tick them off!
Seeing you are calm, competent, take time to listen to and address their concerns, and genuinely care about the child goes a long way in starting to build a therapeutic relationship.
Pediatrics is a really special branch of nursing. It is oftentimes challenging and all the while incredibly rewarding. Be confident but humble. We're all learning; it's okay to ask for help
We learn something new every day (or 10 things!)
All the best!