Perhaps the most important thing to remember about your students' errors is that they are developmental; that is, they are a sign of learning, not a symptom of a deficiency. It takes a long time to learn the intricacies of a new linguistic code. Don't become discouraged if your corrections don't appear to have an instantaneous effect: keep at it. Consistent correction will help the child internalize the correct rules of English.
Finally, set the ESL child up for success, not failure. Recent research shows that the type of task and the role a student is assigned within it predict the errors he or she will make. That is, if the task and its roles are thoughtfully developed with students' skills and limitations in mind, the learner will make very few errors. If the task is poorly conceived or is beyond the current capacity of the learner, there will be many mistakes (Berreta, 1989).