I am helping design an interactive educational toy targeted to the 3-6
year-old range. For this early stage of development, I'm looking for
research on how kids interact with toys. Specifically their attention
span, amount of repetition they like, the types of questions they are
able to answer, and anything else that could help inform the design of
the toy interface
(which is simple and audio based) would be most helpful.

I'm looking for articles or books that may be good reading. I have
already found a good powerpoint
(http://www.cs.umd.edu/class/fall2001/cmsc838s/Chapter9.ppt).

I will accept any good research on the subject.

Have you tried ERIC at http://www.eric.ed.gov/ ?

Try terms such as toys, educational games, attention span, etc. There
is a handy dandy thesaurus for finding the right terms located on a
tab in the upper right corner of the page.