Articulation disorders and phonological disorders are types of speech sound disorders.  Speech sound disorders occur when children have difficulty producing sounds or sound patterns.  Most children make mistakes producing sounds as they learn to say new words.  Your child may exhibit difficulty making sounds or exhibit sound error patterns such as substituting sounds, omitting sounds, adding sounds, or altering sounds.  These errors in speech production can make it difficult for others to understand your child.  When these errors continue beyond the expected age range, treatment may be warranted to improve speech sound productions and overall intelligibility.