Friendly Defender cards are great for apologetics, but they seem a little 'confrontational' for learning church doctrine. I was looking for something FUN.
I've known about Arma Dei products for a while, but just rediscovered them for this purpose.
Cathletics Playing Cards are great for regular card games and for learning some church doctrine as flashcards. Another tool for this is Cathletics KEY Cards. Once the kids have mastered several of these, they're well on their way!
I also made a Catholic Kids TRUTH or DARE card game for learning church doctrine. If they get the truth question right (answers are on the back of the cards) they GET to play a DARE card. The kid with the most cards at the end of the game wins.
If you're on the Arma Dei site, consider A Treasure Chest of Traditions for Catholic Families -- a GREAT resource for ideas!