Of course the easiest is the fly-swatter game, which I've never used a fly-swatter for. A ball for each student to run up to and grab and slam down on the flashcard after you say the word, that's how I've always done it.
A simple one you can do for a few minutes before it gets out of hand is what I call 'ball roll.' You lean up 3-4 flashcards against the wall at an angle and give the student the ball. They have to say the name of what they want and ROLL the ball. If they hit it, great! If they don't...great!
Some of the best games for killing time involve time. Line up 8-12 flashcards in a horizontal line. Then I always go to
and pull up the stopwatch. The student simply has to go down the line and hit each card with the ball, saying each one along the way, often with the teacher or TA's help.
A variation on that one involves crumpled-up paper balls in a basket. Make a circle of flashcards around the basket and put a paper ball on each card. The student has to say the name and throw the paper into the basket.
You've gotta get rid of some of that excess energy from time-to-time and that's why I have 'card run.' Simply put 4 flashcards in the corners of the room and have the students run from one-to-the-next calling out the name. You have to be careful; I've had students fall before.
Those are only five ideas in a world of thousands. Most of the time now I find myself just making up games right there in class. Young kindergarten game learners are unpredictable and ill-behaved. Whatever plans you have going into class should be rudimentary at best. The last thing you want is to be staring at your lesson plan while a bunch of five-year-old's are ready to erupt.