Dean actually does pretty good when he first encounters smols, so it would have gone worse than it did, but not as bad as it could. As seen in Walt’s and Jacob’s first encounters with Dean in various AUs, he’s likely to grab, disarm and then trap, likely in a vase (while Jacob would grab a coffee pot), but he’s also very methodical. He won’t hurt Sam purposely, and will keep him trapped while he figures things out. Chances are, the brothers will figure each other out long before Dean calls Bobby up for advice, and if they didn’t, Bobby would scold Dean and tell him to let the little guy go. 

Idjit.