Hello Sravanathi, 

Both disciplines have ample scope to offer.  However, a microbiologists career options are more diverse and they develop skills that are in high demand both within and outside the country. And if we were to compare job scopes for a pediatrician and microbiologist, a microbiologist can acquire jobs in more number of industries than a pediatrician. For example,  a pediatrician can mostly work in clinics,  hospitals, medical laboratories or may take up teaching. However microbiologists can get employment in several industries such as healthcare organizations,  environmental organizations, forensic labs, food and drink, research organizations, etc. 

Therefore while both courses will provide you with good scope for employment, microbiology has a slight edge over pediatrics and therefore microbiology may be considered as the better choice. 

Hope this helps  :)