Babies have to build up their immune system, which can take years. Babies are exposed to a lot of germs–especially if they go to daycare or are around other kids. This is good for helping build their immune systems, but sometimes it leads to infections and illnesses that require antibiotics.
For babies and young toddlers that take antibiotics, they can end up with diarrhea. So I recommend giving your child probiotics to help counter the effects of the antibiotics in the digestive system.
Culturelle makes powders that you can add to your baby’s bottle or sippy cup. They also make chewables for older kids.