'Not by the hair of my chinny chin chin,'' the three little pigs taunted the big bad wolf. When Anna Van Valin was 4 years old, she pronounced the phrase ''not by the chair of my hinny hin hin'' and unwittingly advanced the study of children's language when she did.

Anna's talk was often observed. Her mother, Dr. Jeri Jaeger, is a linguist at the State University of New York at Buffalo who collects the speech slips that children make in order to understand how they learn language. For two decades Dr. Jaeger has collected data wherever she found available children (and willing parents): preschools, the supermarket checkout line and at home from her three children, Anna, Alice and Bobby (now 22, 20 and 18).

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