Continue breastfeeding as long as you can, for best form of prebiotics. Also introduce all kinds of fruits and vegetables, curd as well slowly.

Yes prebiotics helps to develop immunity in kids as it keeps gut healthy. You can give ripe mashed bananas , regarding milk , mom's feed is the best which is rich in prebiotics , if want to start a top feed can try Aptamil as it's also rich in prebiotics.

Yes, Prebiotics are food for healthy bacteria in the gut, which improves gut function that helps boost immunity. Prebiotics are naturally present in breast milk. And if you are unable to breastfeed then choose a formula which contains prebiotics.