When I was young, must've been under ten, I used to play a card game in my guide group in where the deck was continually recycled and if played "wrong" you had

When I was young, must've been under ten, I used to play a card game in my guide group in where the deck was continually recycled and if played "wrong" you had to add a facedown card from the top of the deck, which replaced the current one. The details are fuzzy, but I remember that we all pretty quickly broke the game by memorizing the full deck after playing through once or twice. So we started playing two decks shuffled together, then three. The point being that kids' brains are magical and memorizing the order of a deck is no big deal if you're having fun doing it. Interestingly the thing which immediately foiled our trick was playing against a different guide group which played three decks, but cut and took away half the stack before playing. Having half as many cards (but a random half) broke all our unconscious mnemonics (which apparently included a radix filter).