Producing speech that is clear, audible, and intelligible to others is a challenge for many children with cerebral palsy (CP) and children with Down syndrome (DS). Previous studies have demonstrated the effectiveness of using the Lee Silverman Voice Treatment (LSVT LOUD) to increase vocal loudness and improve speech intelligibility in individuals with dysarthria secondary to Parkinson's disease (PD), and some research suggests that it also may be effective for individuals with dysarthria secondary to other conditions, including CP and DS. Although LSVT LOUD targets healthy vocal loudness, there is some evidence of spreading effects to the articulatory system. Acoustic data from two groups of children with secondary motor speech disorders [one with CP (n = 17) and one with DS (n = 9)] who received a full dose of LSVT LOUD and for whom post-treatment intelligibility gains have been previously reported, were analyzed for treatment effects on: 1) vowel duration, 2) acoustic vowel space and 3) the ratio of F2/i/ to F2/u/. Statistically significant changes in vowel duration and acoustic vowel space occurred pre-treatment to 12 weeks post-treatment in the CP group, and increased acoustic vowel space was observed in 5 of the DS participants. The present study provides preliminary evidence of intensive voice treatment spreading effects to the articulatory system in some children with CP and children with DS consistent with previous findings in other populations.