How many Card Games are there?
There are Rummy-style games, like Concentration and Canasta, Trick Taking games, like Bridge, and many gambling card games, like Poker and Casino.
Then there are Shedding games, the object of which object is to dispose of all of one's cards, Accumulating games, Fishing games, various forms of Solitaire/Patience, and hundreds more.
(...but especially to be avoided is Exploding Snap,
commonly played by students at Hogwarts.)
Both decks together make up the whole of the current periodic table, with all the key data for each element on the face of the cards, so the players can't help but absorb
(Subliminal learning!)
some of it while their minds are open by having fun.
These should be the only playing cards in the house (or school!)