How do you speak like that?

In our last visit to Danny's house, Alex, who is 4 years old, was sitting with Danny during the visit. Alex was watching the activity and was listening carefully to the teacher and me. In the middle of the visit, Alex asked me," How do you speak like that?" I replied," What do you mean?" He then told me, "Well, I know I can understand you when you talk, but sometimes I can't." Then I realized that he meant that he couldn't understand me when I spoke English. I told Alex that he will soon learn how to speak English in school and was going to be able to be bilingual like me. Alex's eyes were big and he said that he knows one word in English... "Bye!!" So young and so smart!!