gym workout Hilary Duff spandex pilates

She's lucky her mom lives so close, because she's got a built-in babysitter!

Hilary Duff left son Luca with his grandma in Studio City while she attend a Pilates class nearby, and the minute the singer was done with her workout, she rushed to pick up her baby boy and take him home.

The Lizzie Maguire star has definitely shed all the baby weight... and then some! Clad in black spandex pants and a tight white top, Mike Comrie's wife looked skinnier than we've ever seen her!

Hil's about to get a lot more exercise now that her little one is walking!

The other day, the actress tweeted a picture of Luca walking around on the lawn in his diaper chasing bubbles!

They say running around after your kids is the best way to burn calories, so she might not even need Pilates anymore!