phonological development

children make predictable pronunciation errors (not really 'errors' at all, when you stop to think about it) when they are learning to talk like adults. These 'errors' are called phonological processes, or phonological deviations. 

Phonological Processes in Typical Speech Development

Phonological Process Example   Description   Pre-vocalic voicing car = gar A voiceless sound preceding a vowel is replaced by a voiced sound. Word final devoicing red = ret A final voiced consonant is replaced by a voiceless consonant Final consonant deletion boat = bo A final consonant is omitted (deleted) from a word. Velar fronting car = tar A back sound is replaced by a front sound. Palatal fronting ship = sip sh or zh are replaced b y s or z respectively Consonant harmony cup = pup The pronunciation of a word is influenced by one of the sounds it 'should' contain. Weak syllable deletion telephone = teffone Weak (unstressed) syllables are deleted from words of more than one syllable. Cluster reduction try = ty A cluster element is deleted or replaced. Gliding of liquids ladder = wadder Liquids are replaced by glides. Stopping ship = tip A stop consonant replaces a fricative or affricate. easier sounds ; p, m, h, n, w, b, t, d. more difficult sounds; k, g, f, v, "ng" y,  r, l, s, "ch," "sh," j, "th" http://www.talkingkids.org/2011/04/speech-sounds-and-kids-part-2.html http://linguistlist.org/ask-ling/lang-acq.cfm http://www.education.com/reference/article/stages-language-development-first-words/