This just released report (April 2007) seems to agree with many of the findings of the Dec. 2006 Kaiser findings.

More evidence of teen and pre-teen multi-tasking

Kids between the ages of 2 and 12 years old spend more than a quarter of their leisure time doing
two or more activities at the same time. Favorite pastimes among the sample group included reading,
using the computer, spending time with friends, listening to music and watching TV. Kids today have
plenty of leisure time, with 2-to-11-year-olds averaging roughly 68 hours a week, and 5-to-12-year-olds
averaging 58 hours. Toddling 2-to-4-year-olds are true layabouts, averaging 94 hours of leisure time every week.
NPD Group's "Kids' Leisure Time II" report, cited in Emarketer news story)

The Henry J. Kaiser Family Foundation
December 12, 2006

New Study and Forum on Implications of Youth Media Multitasking
The Kaiser Family Foundation hosted a forum and released a new report on media multitasking among young people. The report, Media Multitasking Among American Youth: Prevalence, Pairings and Predictors, is based on data from seven-day media use diaries collected from 694 young people age 8 to 18 years old and quantifies the actual amount of time young people spend multitasking when using media or doing homework.

News coverage of the new study:

Media Multitasking Among Youth

More Media, More of the Time

Report sparks debate on kids and multi-tasking 

Kaiser Family Foundation: Multitasker Focus On TV