NICOLE RICHIE TO KYLIE JENNER - STAY AWAY FROM MY BABY BRO!

Nicole Richie switched into protective older sister mode after her 20-year-old brother hooked up with 16-year-old Kylie Jenner - and now she's warning the precocious teen to keep her mitts off of Miles Richie.

"Nicole doesn't approve of the romance brewing between Miles and Kylie," an insider told Dish Nation-despite the fact that mom of two Nicole has been friends with Kylie's half sister Kim Kardashian since they were kids.

"Nicole was a total wild child in her younger days and she doesn't want to see Miles going down that same self destructive path. Nicole is a straight arrow now and she doesn't think Kylie is a good influence. She especially doesn't approve of how Kylie dropped out of school to supposedly be home schooled. She knows that Kylie and her sister Kendall are huge party hounds. Nicole also suspects that Kylie is playing Miles off of her 'other' boyfriend, Jaden Smith."
Though Kylie was spotted making out with 15-year-old Jaden at Kim and Kanye's May wedding, she and Miles were photographed getting frisky in a car on June 13th.

"Nicole talked to Kylie and told her to back off from Miles," says the source. "She's worried Kylie's going to break his heart. But Kylie got all sassy with Nicole and called her out for her checkered, drug-filled past. As a last resort, Nicole appealed to Kim and her sister Khloe and asked them to intervene and set Kylie straight. Nicole is cool with Miles and Kylie as friends, but she doesn't want them hooking up."