When your 18-month-old speaks fewer than 10 words, your 2-year-old uses no two-word combinations, or your 3-year-old's speech is unintelligible to anyone but the immediate family, should you worry? Is the child merely a slow talker who will eventually catch up to his or her peers, or does the child have a speech or language disorder in need of evaluation and therapy?

Every parent knows that children develop at different rates. There is a very wide range of normal. At 22 months, my niece clearly enunciated complex sentences while at 30 months a boy I know was still uttering only two- or three-word phrases. Like most children, they both developed to have perfectly normal verbal and social ability.

The availability of free or low-cost speech therapy for preschoolers under the federal Individuals With Disabilities Education Act has prompted some parents to seek such therapy for children with articulation difficulties or seemingly slow speech development that are well within the range of normal for their age. This can be unnecessarily stressful for parents and children and a waste of valuable resources.

My twin grandsons had just turned 2 when their parents decided to take a vacation without them. The boys, who were told that Mommy and Daddy were going to the beach, looked at their parents' wedding photograph each day they were gone and said, "Mommy, Daddy, bitch." We laughed at the mispronunciation, but it was clear that the boys got the message and could voice their understanding.

Now, from reading "The Late Talker: What to Do if Your Child Isn't Talking Yet" by Dr. Marilyn C. Agin, Lisa F. Geng and Malcolm J. Nicholl, it is also clear that the boys were well within normal range in their language development. Typically by age 2, children use a variety of two-word combinations (more cookie, mommy work), know at least 50 words and mostly use words to communicate.

Now that the boys are 4, I was reassured by the book that their difficulties pronouncing "L" and "th" and their frequent failure to string two consonants together ("geen" for "green") is also within the range of normal. The authors note: "All children misarticulate sounds in the course of normal speech development. They may use sound substitutions, like 'wady' for 'lady.' They may omit sounds, saying 'baw' instead of 'ball.' Or they may distort a sound, so that 'spaghetti' comes out as 'psketti.'"

The book continues, "Concern arises when these errors continue beyond the time when a child normally outgrows them"—usually by 7 or 8. But the authors caution that some parents of children with what they think are speech delays go overboard in trying to speed development. They write, "Excessive parental concern can also impede the child's language development, and counseling may be needed for the parents."