Resources for the little ones

Hi all!  I noticed that there are no discussions tagged with Preschool.  I'm giving a presentation on Web 2.0 to a cohort of teachers ranging from Foundation Stage 1 (3.5 year olds) to Year 6 (up to 11 year olds).  I'm most interested sharing ways in which they can work collaboratively with students and experts from around the world when completing theme-based challenge projects.  Has anyone tried this sort of work with 3-6 year old students?  Are there any good resources for this age group?