A group of 4 to 18 year old children with Down syndrome (N=62) was presented with a set of working memory tasks, including auditory and visual serial recall of words; standardised digit span tasks and a rhyme judgement task. The serial recall tasks involved pictures of common objects or the spoken names of these objects and the children had to recall lists which varied on a number of parameters, including word length and the acoustic similarity of the object names. It was found that contrary to expectation the children's performance showed significant effects of word length and acoustic similarity, which are normally taken to indicate phonological storage and speech based rehearsal. These effects were found in both the auditory and visual presentation conditions and for the youngest age group. In addition to this evidence for speech based storage in short-term memory there was also evidence of the children utilising visual information in the serial recall tasks. The results are discussed in terms of working memory operation and the implications for memory remediation strategies in children with Down syndrome.