All infants need their inoculations (MMR, polio etc). Parents of toddlers will already have experienced the guilt of a trusting child sitting on your lap, gazing up with big eyes that believe in mum and dad completely and have no idea of the ordeal to come.
Then, a look of confusion as mum or dad grip the leg rather tightly and a white jacketed figure approaches with a big needle and brutally stabs them. Shock, pain, anguish, a look of 'Et Tu Brute?' and a deep realization that your child will never fully trust you again to protect them against the pains of the world…
For travelling, it is really important to get all the critical jabs. Priming the little ones before hand on what will happen (without scaring them) works well. Be ready with a supply of stickers / treats / bravery compliments to distract them immediately before and after the traumatic event.
Oh, and if you are getting two kids done at once, keep the second out of hearing range when the first is done. Maxwell heard Zoe screaming when she got her Japanese Encephalitis jabs which meant he was tense and scared before he even got into the doctors room with typically catastrophic tear-stained results.
The bottom line: Jabs are a fact of life for adventurous travel but little kids don't like them any more than we do. Remember the pain and looks of betrayal don't last for long - especially if your next stop just happens to be an ice cream parlour!