Nothing I said is really an illogical assumption. The father of the kid was taping him crying and laughing at him. If you did't know what was going to happen, wouldn't you have jumped a little to at the sound of the scream and your kid fallen out of a chair... Would you have keeped taping, laughed at him, and followed him around the room as he cried? All that leads me to believe that the father knew what was going to happen.
Remember, little children are frightened and scared easily because they are very trusting. Kids believe in monsters under the bed, they're afraid of the dark, and they believe that ghosts can get them... A grown person would probably jump and then just laugh it off... A child's reaction is going to be radically different, as we've seen here... You can't tell me that the father was taping this and didn't know what was going to appear on the screen, and that he didn't necessarily know that the prank was a bad idea.