As a physician, you will get education and experience in areas that are not in your specialty. You never know when that information is going to come in handy - sometimes we pull things out from the past to come up with elusive diagnoses.
You also have many more opportunities as a physician. I, too, thought I wanted to work with children. About a week into my pediatrics rotation, I knew that I was NOT going to be a pediatrician! I still love working with children, I just prefer them to be unconscious. Had I gone the NP route, I'd have been in a bad way, having to make the specialty choice without really having the experience to know where I best fit in. Another great example is a classmate of mine who was a radiographer, and went to med school to become a radiologist. You'd think that her years of experience in the xray dept would give her a good idea of what that entailed. She ended up in Physical Medicine & Rehab, a far cry from radiology. Many of us "knew" what we wanted to do, and ended up doing something totally different. Medicine gives you that flexibility, and it gives you good insight into the various fields. You can't know what the specialties are like until you're living it.
Medicine will demand a lot more from you than nursing will. It will take more training, but that education and experience are well worth it. I'm glad I made the sacrifices that I did, because I know I am providing excellent care to my patients.
Good luck with making your decision.