Im sure if it was bad for their teeth, it wouldnt be allowed for babies of any age however, baby is meant to be of a certain age before you should use as red has said. It will say on the bottle what the age is. Has it been necessary to give it before every feed or are you doing this as part of the feeding routine? As with anything like that, you shouldnt use for longer than necessary and if symptoms dont improve, always consult your doctor or health visitor as they could suggest something that is more suited to your baby.