Try this positive reinforcement method, which permanently imprinted my nephew with "Sikorsky" for helicopter (the only real helicopter, I am told):
Arrange a fly over at a relatively precise time, have the lad near a portable radio with aviation band capability. Preset the radio at 120 KHz, and you speak to the lad as you fly around the house at the minumum legal altitude. Say his name, then the non-subliminal words you want him to remember until the day he passes on from this world.
My nephew went running down his street screaming, "My Uncle Nick talked to me from the sky!"
The 5 watts you put out will make up for any inaccuracies in the radio tuner, especially from 500 feet or so.
Works like a charm, and if done properly, you will ruin his life as surely as yours was ruined. After all, you could have been a Doctor!