This is because there's citrus acid in citrus fruit (i.e. orange, lime, etc). And some of the baby may be allergic to cirtrus acid, so normally the doctor will suggest you not to introduce orange juice (even nuts...)to baby to try until the baby is 1 years old. For sure, some of the baby wouldn't be allergic to. To give or not to give, is only your choice.
Even if you want to give the baby a try, start with a teaspoon first.