Cousin Love💙💙 pic.twitter.com/u6qo7hnBJA— ROBERT KARDASHIAN (@robkardashian) December 7, 2017
The 30-year-old Rob posted the photo of the two children playing on Thursday. It looks like Penelope is playing with Dream's hair, with a pink piano behind them.
"Cousin Love," Rob wrote in the caption, adding two blue heart emojis.
The 5-year-old Penelope also appeared on her mother's social media pages this week. She went ice skating with her mom and Kendall Jenner. As PEOPLE notes, Kourtney shared a few videos from the outing on her Instagram Story.
Rob often posts photos of Dream playing around and uses an image of her as his Twitter profile picture. While Rob doesn't have an Instagram page, Dream still made an appearance there after Kourtney shared a preview of the Kardashian family Christmas card. Kourtney's oldest son, 8-year-old Mason, appeared behind her.
Dream's mother is Blac Chyna, who was engaged to Rob at one point. Their bitter split reached a boiling point when Rob posted explicit photos of Chyna on social media and she was granted a temporary restraining order.
She is also suing members of the Kardashian family, although she sought to have all the Kardashian-Jenner sisters removed except Kim Kardashian West. She claims they were responsible for Rob & Chyna getting cancelled.