Jennifer Lopez Emme Max

Her American Idol gig suits her well!

Despite looking a tad stern, hot mama Jennifer Lopez stunned while running errands with her twins on Saturday in Calabasas. J.Lo donned a flowy, backless, patterned green and black dress while dropping by Barnes and Noble to buy some books with her five-year-olds.

The kids were spotted the day before on a playdate with Rebecca Romijn and Jerry O’Connell's twin daughters. Max had a cast on then so he must have gotten it removed yesterday before the outing.

Jennifer is most likely trying to spend as much time with Max and Emme as possible before Idol premieres. In addition to her busy TV schedule, she'll also be starring in a slew of films come next year, including the Chilean miners rescue flick and the thriller "The Boy Next Door," in which art will imitate life when she plays a cougar.