Kris Jenner -- About Those Fifty Shades ... Crashes Dakota Johnson & Melanie Griffith's Vacation

Kris Jenner's now tailing other people's famous kids around the world -- instead of her own -- and her latest target is "Fifty Shades of Grey" star Dakota Johnson and her mom, Melanie Griffith.

Jenner is currently third wheeling it with DJ and Mel on their Mexican vacation. Despite being 30-plus years older than Dakota ... the moms are right next to her, proudly flaunting their bikini bods too.

The Kardashian matriarch also hung out with Lindsay Lohan in Paris earlier this month during Fashion Week.

Hey, at least when you hangout with other people's kids ... you don't have to pretend to parent them.