My sister possesses many of the smarts that our parents passed to us, and she taught me that subitizing (that is, per Wikipedia, “the rapid, accurate, and confident judgments of number performed for small numbers of items” – essentially counting objects at a glance) is an important thing for kids to learn. You likely subitize all the time without realizing about it (think about the subconscious counts of your kids and/or their friends that you do at the playground, for instance).
I love subitizing drills and flashcards as much as the next dad, but I’d like to suggest that dice games are actually a more fun way to teach this Critical Life Skill. I realized this as I played Yahtzee with our oldest. Initially she needed to count the dots on the face of a die in order to correctly recognize its value. Rounds took a while. Things sped up as her counting got quicker, and then … she wasn’t counting any more. At a glance she could evaluate what number the dot patterns represented. She subitized. She was a subitizer. And we had some gaming fun in the process.
Yahtzee’s one of those games that you can slowly teach your kids, perhaps starting with one of the Yahtzee Jr. character editions for really young kids. In these versions, you’re just looking to gathering different characters—it’s a good, basic entry-point to the full version. With the full version, you can start with the basics and gradually introduce the strategy: they’re just rolling at first and you’re guiding which dice they keep and which they re-roll; then you’re letting them choose which patterns to pursue (Do you want to go for sixes or for the full house?); then you’re simply observing as they manage their own game … and topping you. Since Yahtzee is quite a bit of luck with just a bit of skill / strategy, you’ll get beat without even needing to throw the game … and your kids will love you for it.
That’s Yahtzee: come for the subitizing, stay for the losses that delight your progeny.