How does a parent know when to get their child glasses?

Screening. Most regular screenings rely on emerging communication skills & include recognition of figures on charts at a distance. This is realistic about 3-4 yrs.Although kids may not grasp the concept until later. Vision can be assessed earlier by skilled personnel using special equipment. Early on, one eye stronger than another may lead to problems. Your pediatrician is watching for this starting at birth.
Screening. At each well child visit (typically once a year) your child will get vision screening and a referral to an eye doctor will be made if needed. Elementary school children may also get screened at school. Babies sometimes need glasses if their eyes do not move together or are misaligned. Talk to your pediatrician if you are concerned about this!