To be honest almost every doctor I've spoken to is now in a specialty they never saw themselves in. From orthopods who wanted to be GPs to a paediatric opthalmic surgeon who swore blind she'd never work with children. None of the first-year students ever think they'll be a GP, 70% will be.
Yes, read around the different specialties, a firm knowledge of professional training will be key to a successful interview, but also keep your feet on the ground. Pass your A-levels, get into Med School and then you'll have a clearer idea about where to go.
For me, that's probably not a paeds job.