The Ball
Soccer balls come in various sizes, proportional to the size of the player using them. Technically, balls come in sizes from 1 to 5, but for organized play, only the size 3, 4, and 5 balls are used. Size 1 & 2 balls are sometimes referred to as skill balls, as they are not used in organized games, but they are useful for developing foot skills. The following chart explains the age ranges for each size:
Hint - especially at younger ages, pay attention to the weight of the ball. While most soccer balls are marked "official size and weight", many cheaper (and sometimes not so cheap!) balls, even from the big names, fall outside the circumference and weight limits. If you have a simple kitchen scale, you can weigh a properly inflated ball. Playing with a ball that's significantly too heavy can hurt a young, growing foot, and make it harder to enjoy the game.
Also - check that the ball is properly inflated. A ball with too much air hurts to kick, while one with too little air makes it harder to control. You should be able to push in about 1/4" to 1/2" inch with your thumbs if you hold it and squeeze. Using a needle gauge to inflate to the lower end of the recommended p.s.i. range as marked on the ball is the most accurate way to inflate a ball.