These cards include the number 1 - 20 with the Spanish written below the number, as well as cards without the Spanish words. You can practice with the Spanish set and then quiz with the set that doesn't have the Spanish words.
They are color coded. Every three numbers share a color and different shade, then this is repeated as you go higher. For example, 1-2-3 are all blue starting from light to dark, then 11-12-13 have the same shades. This is to add an extra sensorial dimension so the child can more easily recall the numbers.
I introduced the numbers 1 - 10 first with my 2nd graders and then moved on to incorporate 11 - 20. They enjoyed it when I laid out the non-Spanish cards and as I called out a number they had to slap it.
You can find 21 - 40 on my site as well, http://www.teacherspayteachers.com/Product/Spanish-Numbers-Flashcards-21-40-1491031