Reddit mentions of Ultra Pro Card Supplies YuGiOh Sized Deck Protector Sleeves Light Blue 60 Count x3

if they're learning how to play still, i'd recommend starter deck: codebreaker, as it's the most recent starter deck and a good place to start learning the game. it's pretty well rounded in terms of the cards in it, while still being basic enough so as to not overwhelm new players with walls of text in the card effects. if they already know how to play, then the legendary hero decks is probably a good pickup. it comes with three different theme decks based on characters from the different series, all basically playable right out of the box. if they want packs to open, then the most recent main booster set soul fusion might be a good place to start, though shadows of valhalla, battles of legend: relentless revenge, or legendary collection kaiba are also good sets with lots of cards that fans of the anime would enjoy. (the links for the four booster sets i mentioned are booster boxes, but you can buy individual packs at walmart or whatever as well if you wanted to mix and match. three or four packs of each set for each kid for example, that way they get a more varied pool of cards to play with and collect if they're less worried about actually playing the game.) i'd also recommend getting some card sleeves and a binder so they can learn to protect their cards and keep them organized, since nobody likes damaged cards. playmats aren't strictly required to play the game, but they are recommended as the game has zones that need to be kept track of for a number of reasons, and having the zones visible helps keep things lined up so you know what's going on. the starter deck comes with a paper playmat, which is serviceable enough for a beginner, but there's quite a few playmats available that have zones that are pretty good quality (they're like big mouse pads, basically) though you can get some that have a wide range of designs on them, even custom made ones, though i've yet to have my own made yet so i'm not sure how that works exactly. only other thing you'd really need are a few deck boxes so they can keep their decks separate from the rest of their cards.