One of my favorite ways to practice this is by using a number line. I think even three and four year olds can have fun with it.
Supplies needed are a number line (in my teacher store I have a Lilly pad number line for $3 if you wanted a fun one to use), 20 cards with the numbers 1-20, and a marker of some sort to go to the point on the number line (I use a frog with my lilly pad number line).
Simply pick a card and start counting up. If you want you can practice counting down as well : )
You can play as long as you want and take turns. You can even practice skip counting too!
