Sleeping Queens. I have never met a kid who didn't love this game. The rules are quite simple, but it's a surprisingly fun play - even for adults.
Carcassonne. This is actually an "adult" game, but absolutely and completely doable for a 6.5 yo (my ds was able to play at 3.5 with some help, and my dd has been playing without help since 5.5) This game seriously ROCKS. And there are tons of expansions you can add over the years if you fall in love with it.
Bohnanza. This game is tons of fun, but better with 3+ players. It's about half competitive and half cooperative.
King Arthur. Fun for older kids (definitely fine for a 6.5yo) and adults. You have to collect cards to buy other cards... to buy other cards! The play is pretty fast.
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