S--- happens... but not under Rob Kardashian's watch!

In a video posted to Blac Chyna's Instagram on Saturday (August 20), the model/personality's 3-year-old son with rapper Tyga, King Cairo, tests his boundaries by saying a curse word.

"S---!" the toddler repeats innocently as he crawls under a bed while holding a cell phone which, luckily for us, is recording.

Kardashian, however, isn't having it. Off-screen he asks, "What? What did you say?"

King crawls atop the bed, where the Keeping Up With the Kardashians star seems to be resting, and replies sweetly, "I said s---."

"No, you can't say that," the father-to-be scolds, gently. "Don't say that. That's a bad word. Mommy's going to get really mad at you."

"But I can say s---?" the young boy tries again, before talking excitedly about the "a-sgusting" (i.e. disgusting) things he found under the bed.

"No, you can't say that," Kardashian, who is expecting his first child with Chyna, calmly tells him.

"I've had this video for a min & it cracks me up!" Chyna captioned the video on Instagram.

"Ive been hesitant to post it because I know the media would make it something it's not. But Idc it's too funny," she added. "My favorite part is when Rob jumps out. Look at his face. But overall I'm so happy & blessed to have Robert here willing to help teach King right from wrong."

Watch the cute clip, below:

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