It is important to confirm a diagnosis of respiratory allergies through a medical consultation before giving any antihistamines to a baby. If a baby has a congested or runny nose, it is recommended to regularly wash the nostrils with a saline solution. Antihistamines are available over the counter at pharmacies, typically recommended for children aged 2 and above, but can also be given to infants if necessary. Some antihistamines require a prescription from a healthcare provider. It would be helpful to know more about the specific symptoms experienced by the baby.