They know the most well known Pokémon thanks to merch and a few old cards that my wife and me had when we were children and conserved.

My oldest watched a few episodes when she was 5, and “read” a Pokémon manga after (she watched the images, she didn’t know how to read). I promised her that I will teach her how to play the cards when she’ll know how to read … I will keep my promise and buy her her own deck for her 7th birthday :-)