Watering in our eyes can occur to to excess production of tears or blockage in the drainage apparatus (see the picture).
Excess production is common in older children and most often occurs due to allergic conjunctivitis. Other causes may include foreign body in the eye, infective conjunctivitis, corneal disorders etc.
Blockage of the outflow occurs most commonly in infants, by birth. Typically it occurs in one eye, associated with yellowish discharge at times. Most often this is a self resolving condition & clears on its own with out any intervention by the age of one year. Massaging the sac area will help in some cases. If the symptoms persist beyond the first birthday, a minor procedure called Probing can be done.