I would suggest talking to pediatricians and nurse practitioners about their jobs. In the end, both are quite similar - they see patients, and provide treatment. Nurse practitioners usually practice under the supervision of a doctor. Some patients will be too complex for a nurse practitioner to see, and are best referred to pediatricians. The training process is considerably shorter (and less expensive) for a nurse practitioner than a physician.
The idea of becoming "a nurse practitioner first" doesn't work that well in practice. Although it's certainly possible to do this (and I've known several who have), you don't get any advanced credit in medial school or residency for the nurse practitioner work you have done - it will still take just as long (and cost just as much) to finish medical school. And medical school is definitely full-time - you won't be able to earn money as a nurse practitioner while you are in medical school.