Well, Vincent doesn't exactly have arms, and he doesn't want to put Phalanx down just yet (acting under the "the floor is lava" clause of child-handling etiquette, wherein scared kids will sometimes start freaking out if you try to make them stand on their own two feet after being held).

So he does the next best thing. He just sits on him.

Plunks himself right down as if Robin was an over-sized pillow. That gets the demigod to wake up, blearily wheezing to consciousness as he tries to figure out what heavy thing is suddenly pressing down on his solar plexus.

"Hey," Vincent deadpans at Robin, "Your kid had a bad dream or something."