Way before they were appointed Hollywood's golden boys for their Oscar-winning Good Will Hunting screenplay in 1998, Ben Affleck, 34, and Matt Damon, 36, had each other's back. "Ben's really loyal and really honest, really smart, really funny," says Damon. And we wouldn't be surprised if these childhood buddies from Cambridge, Mass., carry their friendship over to the next generation – to Affleck's 10-month-old daughter Violet and Damon's 4-month-old Isabella.