A new tool to measure changes in random dot stereoacuity development from 6 months to 5 years of age was developed and tested. Either a forced choice or operant preferential looking (PL) paradigm with a happy face target was successfully used to test 136 children. Results indicate that stereoacuity measurements continue to develop through the first years of life. Although children below 24 months of age can be expected to have stereo thresholds in the range of 300 sec arc, there is a transition at approximately 24 months of age after which stereoacuity approaches adult levels. The sensitivity of this test in detecting binocular vision problems was 80%. These results provide guidelines for the assessment of stereoacuity in young children and also provide a new tool for the early detection of binocular vision anomalies.