Playing cards or other numbered cards can be reused to practice number skills and math skills.
You can use any playing cards...just take out the face cards. I've been using Uno cards, since the numbers are large and focus on single digits.
For pre-K and kindergartners, use them to practice numeral recognition. They can sort or match the numerals; talk about each one. As they count or group objects into quantities, show and say the numeral.
As kindergartners gain more skills, show a card and ask them to count out that many objects. Show another card and count objects. Then compare the two quantities.
If you create your own board game, you can use these cards as part of the game. Draw a card and move a game piece that number of spaces on your game.
Or draw a card and find that many items in the room that share a common characteristic (color, shape).
For older kindergartners, draw three cards. Help the child put the numerals in order from least to greatest. (I played this game with first graders last year.)
Use the cards for part-part-whole skills. Lay down a 5 card and count out the objects. Divide the objects into two groups and locate the numerals for those amounts. (For example, 1 and 4.) Seeing these parts of a larger number builds skills in addition and subtraction.
Another reason I like using Uno cards is that I can use the cards to make larger numerals. I can put 2 card and 3 card next to each other for 23. If you have a child interested in numbers, you can create any number by placing the cards next to one another. (And Uno cards have a 0!)
But note. Whatever you are doing with your kids, keep it fun...as a game. Don't drill or force the play. Start a game. If a child gets engaged, keep going. If the child seems interested in something else, put it aside. You have introduced a concept; build on it when a child's interest is high.
What ideas do you have for using cards with numbers?