Most children produce errors in their speech as they learn to say new words.  A speech sound disorder (articulation disorder) occurs when these errors persists past a certain age.  Each sounds has a different age range for when it should be correctly produced.  By age of 8, children should be able to correctly produce all sounds in English.

Please click on the link below for speech development norms:

https://www.twomeyspeechtherapy.com/lib/pdf/Speech-Sound-Development.pdf