Practice throwing and catching the ball. (a game loved by most!)
Tell your child that you will take turns saying a number when you catch the ball. For example when you throw your child will say 1 then when you catch you will say 2 and so on. Set a goal and say "let's see if we can count all the way up to 20! without dropping the ball!" If you drop the ball you start all over again.
You can make this game easier or harder depending on the age and ability of the child. For example to make it more challenging you can count in 2's 3's 5's 10's etc. You can also extend the game to end at a higher number. (count by 3's all the way to 99!) You can also stand further away from each other to make the catching and throwing challenging.
To make the game easier you can count up to 15, 10, or 5. If your child is having a hard time catching come closer to each other.