Here are some signs that you can look out for:
- Frequent rubbing of eyes
- Excessive blinking
- Tilting of head or squinting when reading or watching TV to see better
- Headaches from eye strain
For more information, you can take a look at this Healthchange article:
http://www.healthxchange.com.sg/healthyliving/childrenhealth/Pages/Childhood-Myopia-Tips-for-Parents.aspx