Kourtney Kardashian is killing it in a crop top for mommy-and-me class!

The sexy mother-of-three wore a skin-tight white crop top -- leaving NOTHING to the imagination -- and some unusually high-waisted sweatpants with black Vans, on Tuesday, for an outing with Penelope and little Reign.

Now, Kourt's not fooling anybody ... we know high-waisted pants with a crop top means, hiding those love handles and maybe some left-over wrinkles from the less-than-taught tummy after carrying three children. But you know what? Who cares! She looks great!

And she's obviously trying to look her best, with baby daddy Scott Disick off in Miami making out with some random girl in a hotel pool. Poor Kourt! Scott was photographed with model J Lynne (who the hell has ever heard of her?), her legs spread around his waist, Scott leaning into her neck for the make out. So we asked what Kourtney thinks about Scott's tropical tryst and here's what she said ...