The problem you describe is fairly common with young children suffering from a common cold
. His watery eye is due to retrograde infection from the nose travelling up the nasolacrimal duct
that connects the eye and nose. use warm compresses ( a washcloth soaked in warm not too hot water and squeezed) along the part on the side of the nose just below the inner angle of the eye where the duct exists. approximately 10 mins 4 times a day. you may also gently massage
the area moving in a downward direction from the inner eye angle down the side of the nose using your little finger. this helps drain the fluid back into the nose. though this sounds viral ,to prevent a superadded bacterial infection try CHLORAMPHENICOL eye ointment also available in applicaps in the affected eye just at bed time. this may be continued for around 5 days. The watering usually resolves along with the runny nose.