I have a four year old twin (girls) they are identical twin. I have noticed this since birth that whenever twin A falls sick, immediately she gets bet
All those popular beliefs about treating twins even if only one is sick are pure myths and fables
Some infectious diseases of course are contagious or perhaps both are exposed to the same thing causing the illness eg mosquito bites causing Malaria. However DO NOT TREAT A CHILD IN ANTICIPATION!! Always wait and then see a doctor! Never assume it is the same illness. You may be wrong! It is also not automatic that the child will be sick at all