Histazine should only be given to children over 6 months. It has serious adverse reactions to the infants. It could cause severe respiratory depression (inadequate, shallow breathing, decreased respiration) and periods of apnea. Watch out for central nervous system (CNS) depression, too. The signs are vomiting, somnolence, seizures or hyper-excitability and lethargy.
Please notify your pediatrician ASAP.