A study involving 117 six year old children and 104 eight year old children has found that the ability to preserve information in working memory begins at a much younger age than had previously been thought. Moreover the study revealed that, while any distraction between learning the words and having to recall them hindered recall, having to perform a verbal task was particularly damaging. This suggests that their remembering was based on “phonological rehearsal”, that is, verbally repeating the names of the items to themselves. Consistent with the research suggesting children begin to phonologically rehearse at around 7 years of age, the verbal task hindered the 8 year olds more than the 6 year olds.
(2010). The development of memory maintenance: Children's use of phonological rehearsal and attentional refreshment in working memory tasks.
Journal of Experimental Child Psychology. 107(3), 306 - 324.