updated 12/16/2013 AT 7:00 AM ET
•originally published 12/16/2013 AT 8:00 AM ET
After having two children in not even two years, Jessica Simpson says she is back to her pre-pregnancy weight thanks to Weight Watchers and chasing children.
“With both kids I’m running up and down my stairs a million times,” Simpson, 33, told USA Today. “Kids can keep your metabolism going.”
Simpson has two children with former NFL tight end and fiancé Eric Johnson: a daughter, Maxwell, born May 1, 2012, and a son, Ace, born June 30, 2013.
“Eric and I go on walks together,” she said. “I try and walk about four miles a day consistently. It makes me feel better.”
As does Weight Watchers. Simpson said she has lost more than 50 pounds after Maxwell was born, and she “jumped back on Weight Watchers” with their Simple Start program after her doctor gave her the okay following Ace’s birth.
The actress and fashion mogul, who admits she is not “good at chopping” vegetables, has someone help prepare family meals, and she also works out with personal trainer and PEOPLE.com blogger Harley Pasternak four days a week for nearly an hour.
But perhaps Simpson’s favorite exercise? Doing somersaults in the backyard with Maxwell.
“Every day we don’t know what’s going to happen,” Simpson said about her young family. “They definitely keep our lives busy but full of smiles. We laugh a lot.”
Which isn’t always easy, considering the constant media attention on her weight.
“It does get old having people harping on how much you weigh or your body after pregnancy,” said Simpson. “People are going to pick me apart no matter what I do. I’m always going to have critics.”
Simpson told USA Today that she was on a mission “to be the best version of myself. I want to be a great mom and a great example to my kids.”
Simpson said that she and Johnson are currently planning their wedding and that she has been “pulling all kinds of sketches for dresses and colors.”
As for the possibility of expanding the family after the wedding: “I can’t even think about being pregnant again,” Simpson said, before quickly adding, “I would never say never.”