Many of the children I work with have a delay with phonological processes.  Phonological processes are normal error patterns in children's speech development.  They are error patterns that normally developing children experience.  When they do not disappear by the expected age these processes impact speech intelligibility and often lead to a need for speech services.  Here is a link that explains some examples as well as the age when these errors should no longer be observed. https://www.speechandlanguagekids.com/phonological-processes/