Thanks for your query.
As far as possible any antiallergic like chlorpheneramine should not be used in child below 2 yrs without the doctors advice.
Though in India it is frequently used for allergies,and rhinitis
If given in a proper dose it does not cause any major problem other than sedation.
Since it is a allergic reaction
it has to be treated so I would suggest you to consult a Paediatrician before giving medicines.