By the age of four, most children are able to create most of the sounds required for speech.
But, some children may have trouble forming certain sounds, or saying longer words. Sounds like ‘k’ and ‘g’, or the ‘v’ sounding like ‘b’ instead.
Other children can have difficulties pronouncing consonant clusters which are groups of letters with no intervening vowel sounds.
For typical development of speech sounds, read Speech Pathology Australia's Fact Sheet on Sound of Speech for Pre-School Aged Children.