Young 19-year-old Sofia Richie, a kid herself, played mom to boyfriend Scott Disick's three kids on Saturday, as she carried little Reign to the car after a sushi lunch date at Nobu Malibu. These days, when Scott has weekend custody, it comes along with a built-in babysitter, his teen girlfriend Sofia ... and we're pretty sure the kids' mom Kourtney Kardashian HATES seeing pictures like these. Sorry, Kourt! We'd be pissed, too!