Photo SpecialSneak Peek! Child Stars: Then & Now

MAYIM BIALIK

Now: She hit the books – hard – earning her Ph.D in neuroscience at UCLA last year. "My thesis has a long, pretentious-looking title," says Bialik, 32. While she still reviews grants, Bialik jumped back into acting with roles on Curb Your Enthusiasm and Fat Actress. This fall, she's expecting her second child with husband Michael Stone. "I'm working overtime being a mom," she says. "But I'd love to do a sitcom again."

To find out where more of your favorite child stars are – Kellie Martin! Wil Wheaton! The Boy Meets World cast! The kid from Charlie and the Chocolate Factory! – pick up PEOPLE's Child Stars: Then & Now, hitting stores June 23!