The things mentioned on this thread - disliking adults and their health problems, liking the positive attitude of children, and enjoying the chance to interact with children were all major aspects of why I originally went into pediatrics.
Over 25 years later, what makes me most glad that I went into the field (other than the fact I still don't care to take care of adults) is that I truly believe that we need advocates for the health care of children. I am grateful that when I participate in national committees and health policy, I do so representing the interests of children who have, both literally and in terms of the number of advocates, the smallest voice in most health care policy debate processes. This allows me to shout a bit louder. In a typical poiicy committee that I participate in, 80-90% of the discussion is about the effects of the policy on adults and their health needs, the cost of delivering health care to adults, etc. I like to be able to have learned what is unique about children and to be their advocates, as individuals and as a group.
This is fresh in my mind, because, as an "oldbear" I spend a large amount of time these days doing public policy type activities. Pediatricians are tremendously respected for their role and for advocating for children. The AAP isn't a perfect organization, but we can be proud of its role in speaking up for children.
Pediatrics isn't for everyone, and med/peds is a great alternative for many who enjoy both children and adults and are interested in fellowships or hospital-type care as well as general practice of medicine and pediatrics. But, I know of very, very few people who have ever regretted doing a pediatric residency. Sure, some don't like where their career ended up. Some may envy those who make more money, etc, but few regret training in pediatrics.
Don't let others decide this for you. It's not that bad to drive an old Subaru. I like mine just fine.
So, think about whether kids are your favorite patients. Think about whether a career of fighting the system, and occasionally parents, for the sake of kids is what you want to do. Then go for it!