Very few cons. Vaccines are safe for most kids. The worst reaction most children have is fever, some irritability, soreness, and redness. It's a small price to pay for not getting potentially serious diseases like measles, flu, and whooping cough. Getting shots helps protect other people, including siblings, from those illnesses. Babies too young to get whooping cough shots have died when exposed to it.
Mostly pros. Immunizarions are safe, effective and have minimal real side effects. The diseases they prevent can be deadly.