The webisodes, produced by children's media company A Squared Entertainment, last for up to five minutes.
'Secret Millionaire's Club', featuring Buffett and 'GiGi & the Green Team', featuring Bundchen, are scheduled to debut on AOL in autumn, while 'Little Martha', starring Stewart and 'Kosmos', inspired by the late US astronomer Carl Sagan, are to launch in spring 2010.
In 'Secret Millionaire's Club', an animated Buffett is mentor to a group of kids who have adventures in business and learn financial lessons along the way.
'Gigi & The Green Team' features an animated Bundchen, who lives a double life -- supermodel by day, superhero protector of the environment by night. The series will educate, entertain, inspire and empower girls to protect and preserve the environment.
'Little Martha' (working title) features a 10-year-old animated Stewart who operates an event planning company from her tricked-out treehouse. Together with a group of friends, she teaches kids about cooking, crafting, and gardening as they create unforgettable events together.
'Kosmos' features an animated Sagan, inspired by the science series, 'Cosmos' and developed by its co-creator Ann Druyan. 'Kosmos' will combine real science with action and adventures set in space.
Andy Heyward, co-founder of A Squared, said: "We are privileged to have some of the premiere icons of our time to inspire modern content for children.
"Each an expert in their respective fields, these celebrities have committed to bringing content with a purpose to kids.
"Together with AOL, we are reinventing the way multi-media brands are launched to connect with kids throughout their multi-tasking daily lives."
Heyward, a longtime creator of children's entertainment, founded A Squared Entertainment with Amy Moynihan, a veteran of brand marketing, earlier this year.
Buffett said: "What better time to help educate our kids about financial responsibility. Andy Heyward and I have a longstanding relationship, and I am excited to introduce a series that is as fun as it is informative."
In addition, AOL is working with MGX Lab to create games and activities to support and extend the webisode content.
Tim Armstrong, AOL chairman and CEO, said: "AOL has a proud heritage of providing families and children with high-quality educational and entertaining online content, and we're delighted to work with A Squared to bring these innovative programs to our users and across the web."