Rob Kardashian is a "doting stepfather" to Blac Chyna's son.

The sock designer was spotted at Sky Zone Van Nuys, a trampoline park in Los Angeles, this week with the tot, where the pair spent almost three hours together.

A source told PEOPLE that "that they were having a blast together, with Rob holding King's hands while he jumped on the trampolines".

The insider added that Rob, 29, is a "doting future stepfather".

Meanwhile, Rob's mother Kris Jenner recently told his sisters Khloe Kardashian and Kim Kardashian West to "f**k off" when they slammed her for paying for his new house.

The 60-year-old matriarch was urged to "cut the cord" and "drop" the sock designer by his older sisters, but Kris insisted they should keep their opinions to themselves.

On the upcoming premiere of season 12 of 'Keeping Up With the Kardashians', Kim said: "You should not be paying for your son that is almost 30 years old to buy a house."

Khloe added: "Drop him. Cut the cord."

But Kris hit back and told them to "relax" and mind their own business.

She said: "You guys can judge me all day long, I came here to have a nice dinner, so just...everybody relax.

"You all have to have somebody to blame and criticise instead of saying, 'What's the problem?'"

After Kim told her that she was the problem, Kris then told her daughters to "f**k off".

She blasted: "No, all of you can f**k off and go think of something else to talk about. I've seen you guys through so much s**t that you do that I have to f***ing put up with."

Kris helped Rob to purchase his new $2.8 million home in Calabasas, California in February, a month after he was kicked out of Khloe's home over his relationship with Chyna.