how to prevent

Wear thicker clothes and make sure that he is warm. Do not go outdoors as well. Praying for your baby's health.

I don't know how old your baby is, so I don't know what he can eat. He should be given lots of vitamins to make sure his immune system is good. Then yes, if he stays indoors there are less chances to get a flu. Make sure to cover him well, especially the nose/mouth, if you have to go outdoors. And always disinfect whatever he can easily grab, touch and bite.

Use room heaters to get warm temperature.

He's still a baby so you need to see a doctor he's sensitive to everything he does not have a strong immune system yet.

Stay indoors