This activity was originally used for my 1st year junior high students, but can be used for any grade that can count up to 40.
There are four "levels" with 7 questions overall. For the first three levels, the students will have ten seconds to look at the image before it disappears. There is also a timer animation that you click to start. They are then asked "How many?" of something in the image (ex: How many colored pencils? How many blue flowers?). For the last level, the students will watch an animation and count how many birds fly across the screen (no timer).
I played this with groups in class. After looking at the image/animation, each group had a chance to guess "How many?". Any group that got it correct got one point, or if no groups got it, the closest got one point. Some of the questions were pretty difficult for the students, but the focus was less on getting the exact number right, and more on them practicing many numbers.