give your child supplements like immuped or sambuc, let your kid play under the sun often, go to the park and run freely, eat fruits like kiwi and berries in the morning. it worked for my kid.
Babies have weak immune systems, making them susceptible to infections. Breastfeeding is a good way to strengthen a baby's immune system.
Can you let us know more? How old is your baby? Was he/she born prematurely/ underweight?