A pediatrician is a medical doctor. All medical doctors must complete medical school (4 years). Prerequisites for medical school include at least a four year undergraduate degree (usually biology and chemistry). After medical school a we must complete a residency. The residency for a general pediatrician is three years. Becoming a pediatrician takes several years like other medical professions.
Typically, you get your GCSEs, then A levels. Then you go onto do a 5 or 6 year degree in medicine at university. Following this, you do 2 years foundation training; this basically links medical school to specialist training. The next step is your specialist/GP training which, depending on what area you wish to focus on, could take anything from 3 to 7 years.