Your child is too young to know that he could have a vision problem, so you'll want to be attentive about noticing signs of potential trouble. Contact his doctor if your child: 

• Holding objects up close to his face to see them frequently and more than just the normal exploratory nature of toddlers 
• His eyes seem to wander or looking elsewhere than where they are indicating
• Tilts his head to see better (while looking at a picture, for example)
• Rubs his eyes when he's not sleepy
• Seems to tear excessively
• Closes one eye to see better (while looking at a book, for example)
• Seems overly sensitive to light
• Eyes that appear obviously crossed or off center
• Has redness in his eyes that doesn't go away in a few days, sometimes accompanied by pain or sensitivity to light
• Pronounced clumsiness or stumbling or even failure to see objects on a regular basis
• Has a persistent, unusual spot in his eyes in photos taken with a flash (instead of the common red-eye, for example, there's a white spot)
• Has a droopy eyelid that won't ever fully open
• Has white, grayish-white, or yellow-colored material in the pupil of his eye 
• Has bulging eyes
• Complains of eye pain frequent headaches

Your child's doctor can help you determine whether you should be concerned. She may examine your child's eyes, screen his vision, or refer you to an eye specialist (ophthalmologist).