A person can qualify as a licensed practical nurse in one year. Registered nurse programs take two, three, or four years. Specializing for nurses is largely a matter of experience rather than formal education. However, a nurse can take a Master's Degree in a specialty, such as pediatrics, and then be designated a "Pediatric Nurse Practitioner." Requirements for nurse practitioner status vary from state to state. It's best to check with a local college or university that has a nursing degree program to get information for the state where you live.
It is my understanding that you have to have your RN degree (usually 2-4 yrs) then you can get a job that specializes in pediatrics to get your training. I was told that basically RN's are trained to be able to do anything in the healthcare setting, but you get your specialized training hands on.