As seen in this Instagram video posted by the E! star on Monday, the little fella took it upon himself to playfully hit his fellow family member on the head with what appears to be a red hat.
"Mason!" Khloé exclaims with a laugh following the 4-year-old's silly smack.
But clearly there were no hard feelings.
"I love being an aunt!!!! #AuntieKoKo," Khloé captioned the clip.
Speaking to cohosts Mel B, Jules Lund, Sophie Monk and Merrick Watts, the 29-year-old was refreshingly candid, saying, "It's definitely not anything I'm through. I'm going through it, but I'm not through it."