Kylie Jenner Tattoos Her Initials on Lionel Richie's Son [VIDEO]

Kylie Jenner helped tattoo her initials on the hand of Lionel Richie's son ... which is both stupid and not entirely legal ... and TMZ has the video.

It all went down at a recording studio in Hollywood on Friday night. According to our sources, Kylie was there with sister Khloe Kardashian, French Montana and Miles Richie.

We're told Miles (who is 19) was getting ink from John Petro, who has tatted up the likes of Soulja Boy and Lil Wayne ... when Kylie decided she wanted to help out.

Sources say Kylie threw on some gloves and put her hands on top of Petro's as he administered the tat -- sorta like when a father lets his kid sit in his lap and "drive" a car.

But according to the LA County Dept. of Public Health, only people over 18 can give tattoos -- or even participate in the process -- and Kylie is only 16.

If authorities decide to go after Jenner, she could be hit with a misdemeanor and fined up to $1,000 ... and Petro could have his license suspended.

As for Richie ... well his punishment lasts for eternity.