In most cases an apartment complex cannot make rules which restrict children from playing with a ball because a window may be broken. If a child breaks a window, then it is the responsibility of that child’s parents to pay for a new window. However, the apartment is not allowed to make rules restricting children from playing with a ball because the apartment owner does not want any windows to get broken.
Rules prohibiting children from playing on the grass areas because the grass may be killed or a sprinkler broken are illegal. If a child breaks a sprinkler, then the parent can be asked to pay for the replacement cost. Just about any rule which prohibits children from playing in the grass common areas will likely be found to be illegal.