Term used to describe a problem in acquiring a first language in childhood on a normal schedule.

The milestones of child language development— the onset of babbling, first words, first sentences—are quite variable across individuals in a culture, despite the universal similarity in the general ages of their development. In one study of 32 normally developing children at 13 months, the average number of words reported by parents was 12, but the range was 0 to 45. The two-word-sentence stage was reached anywhere from 16 to 28 months in the same sample. In addition, differing styles of language development are now recognized.

Some children fit the classic pattern of first speaking one word "sentences," such as "truck," then joining two words "truck fall," and then three, "my truck fall." But other children...