Reese Witherspoon and Vanessa Minnillo have wasted no time getting back into their skinny jeans after both giving birth just a few weeks ago.

Witherspoon, 36, and her talent agent husband, Jim Toth, welcomed their son, Tennessee James, on Sept. 27, and Witherspoon was already spotted out in Beverly Hills on Thursday in a pair of form-fitting jeans that showed off her once-again petite figure. 

(View pictures here.)

It is likely that the actress whipped her body back into shape through a daily regimen of yoga and running, as she is often photographed by the paparazzi running or carrying a yoga mat. 

According to healthy living site Fitsugar.com, in February, Witherspoon told US Weekly, "I work out all the time anyway just to stay healthy. I don't believe in crash dieting or anything like that."

The "Legally Blonde" actress also has two other children from her previous marriage to fellow actor Ryan Phillippe.

Like Witherspoon, Vanessa Minnillo has also slimmed down quickly after giving birth to her son, Camden. She was spotted in Los Angeles on Wednesday looking lean in a pair of skinny jeans. 

(View pictures here.)

It is likely that Minnillo lost the weight through a restricted diet, as she did an interview for the website SheKnows.com last year about her health regime and revealed that she has not always been health-conscious, but she and Nick “love to have ‘cheat days.’ She went on to say:  “As I've gotten older, I realize it's harder. You have to be more careful about what you put in your body because everything affects you differently. 

"I've always taken multivitamins. Every morning Nick and I take our vitamins together. Through my multi I didn't realize I was getting all the folic acid I needed.” 

Minnillo went on to admit that she is not into cardio. Instead, she said, “I like a multi-purpose workout. If I can do lunges and dumbbell curls at the same time, I'm all about it -- something that doubles up and works more than one muscle group. 

"I like using the elliptical machine and working out my arms. I like to feel the workout from head to toe,” she said.