Goofs

I do believe the lack of a game cartridge when the younger brother is playing game boy is intentional and not a real goof, it is his power to play the game and if there was a real game then he'd be playing that instead of 'real' life. It's just the device he uses. Having a game cartridge in it would have been pointless and on a tad bit on the marketing side of filmology. Maybe they didn't have a backer or couldn't afford to have a real game with all of its infringements with it carried over onto the film itself.