There is a typical pathway of speech development milestones that occur across a young child's journey towards using correct speech sounds when talking. At one year of age, babies start saying their first words. By two years, many children start combining words and can be understood around 50 per cent of the time by strangers. By four years, children are using full sentences, and their speech clarity has significantly improved such that, although they still often have some slight sound errors, strangers can understand their overall speech 100 per cent of the time.

In their speech, children use predictable patterns of errors (known as phonological processes) that make sounds easier to say while they are learning to say them correctly. For example, many parents will have heard their young child say "wing" instead of "ring" or "nana" for "banana". These speech sound error patterns gradually decrease over time, with most eliminated around five years, up until around seven years when a child should have no errors left.

Delays in reaching these milestones might indicate a speech sound disorder or phonological impairment in which a child needs intervention from a speech pathologist to help them learn how to say certain sounds correctly.