Speech sound errors occur naturally as a child develops speech. However, when speech errors continue past a certain age, they may have a speech sound disorder. Every sound has an age range in which a child should develop that sound correctly.

5% of US children between the ages of 3-17 have a speech disorder and the prevalence of speech sound disorders (articulation and phonological processes) in young children range from 8-9%.
Speech sound disorders are more prevalent in boys than girls.
Speech sound problems on their own are the most common individual type of communication disorder.
Most 2 yr olds are 50% intelligible, 3 year old at least 75% intelligible, and most 4 year olds are 100% intelligible.

Speech sounds delays may be attributed to problems with the child’s oral structures (tongue or roof of the mouth), hearing loss (including frequent ear infections), learning disabilities (the brain works differently), developmental disorders (autism, cerebral palsy), and extreme environmental deprivation.

References:

National Institute of Deafness and Other Communication Disorders/US Department of Health and Human Services

https://www.asha.org/public/speech/disorders/SpeechSoundDisorders/

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