Does my child have to be able to read before I take them to the optometrist?
No. There are tests that can be used with 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 even if they are very young. 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.