Kevin Federline, 29, knows taking the kids would shatter Britney Spears, he's worried for their safety and insists money isn’t his motive, LIFE & STYLE WEEEKLY reports.

Why Kevin Federline wants the kids

“Kevin believes his children are in danger, and he wants to save them,� says the insider close to him. “This is about who can provide a safe, secure and stable environment for the boys. So he wants to know how she treats the kids when she has them. Does she diaper them? Does she read to them? Is she drunk when she’s with them?�

By calling her friends and family to testify, “he’s trying to prove that Britney’s not a fit parent and that it’s not safe for the children to be around her,� says LA lawyer Steve Cron, who does not represent Kevin. “Britney seems unable to control her actions, so Kevin has a good case.�

In fact, Kev’s convinced he’ll win. While Britney’s been out drinking night after night, “he’s been keeping his nose clean, lying low and following his lawyer’s advice,� a friend of his says. “Kevin says Brit’s already lost custody of the boys. There’s no way she can win.�