25. A system for of assessing a key child's language development, comprising: a processor-based device executing software comprising: an application having an audio engine configured to process an audio recording taken in the key child's language environment to identify segments of the recording that correspond to the key child's vocalizations; an adult automatic speech recognition phone decoder configured to process segments that correspond to a key child's vocalizations to identify each occurrence of each of a plurality of phone categories, wherein each of the phone categories corresponds to a pre-defined speech sound; and an expressive language assessment component configured to determine a distribution for the phone categories and using the distributions in an age-based model to assess the key child's expressive language development, wherein the age-based model is selected based on the key child's chronological age and the age-based model includes a weight associated with each of the phone categories.
25. A system for of assessing a key child's language development, comprising: a processor-based device executing software comprising: an application having an audio engine configured to process an audio recording taken in the key child's language environment to identify segments of the recording that correspond to the key child's vocalizations; an adult automatic speech recognition phone decoder configured to process segments that correspond to a key child's vocalizations to identify each occurrence of each of a plurality of phone categories, wherein each of the phone categories corresponds to a pre-defined speech sound; and an expressive language assessment component configured to determine a distribution for the phone categories and using the distributions in an age-based model to assess the key child's expressive language development, wherein the age-based model is selected based on the key child's chronological age and the age-based model includes a weight associated with each of the phone categories. 30. The system of claim 25 , wherein the audio engine is configured to segment and assign a segment ID indicating a source to a first plurality of audio segments derived from the audio recording, the segmenting and assigning performed using a Minimum Duration Gaussian Mixture Model (MD-GMM), wherein the MD-GMM includes a plurality of models used for matching to the first plurality of audio segments, the plurality of models including a noise model that includes characteristics of sound attributable to noise, a key child model that includes characteristics of sounds from a hypothetical key child, and an adult model that includes characteristics of sound from an adult, wherein the segmenting and assigning assigns a portion of the first plurality of audio segments to the key child's vocalizations.