There are tests that can be used on infants and preschool children who cannot read. If you have any concerns about your child's vision you should find a local optometrist who will test their vision. However, if you have no concerns, it is perhaps better to wait until your child is a little older – say around three and a half years – before taking them for a full eye examination.  Even if your child's vision seems good it is worth taking them for a full sight test at a qualified optometrist when they reach school age, just to make sure that there aren’t any issues with their vision that are likely to affect their early school years.