Professor Beef said:Your son means "Soul Silver." It's the same game but with different Pokemon to obtain. Action Replay lets you generate any Pokemon into the game's storage system, duplicate items, manipulate levels of your team, etc. I have no clue if it's 3DS-compatible, but until I'm proven otherwise I'll say "no."
As for other Pokemon games, there are Black/White. And if he wants to try something different, get him one of the Pokemon Mystery Dungeon games. They're roguelikes with a Pokemon coat of paint.
don't forget about Pokemon Platinum, either, if he hasn't played it. it's an entirely different game (if he hasn't played Pokemon Diamond/Pearl)