The baby in the story wants to catch the ball that was thrown by the children playing outside. The story "What's in the Mailbox?" is about a baby who is eagerly waiting for the mailman to arrive. However, while waiting, the baby sees children playing outside and becomes interested in the ball they are playing with.

Heading 1: Summary of the Story
The story "What's in the Mailbox?" is about a baby who is waiting for the mailman to arrive. While waiting, the baby becomes interested in a ball that the children are playing with outside.

Heading 2: The Baby's Desire to Catch the Ball
The baby in the story is shown to be interested in catching the ball that the children are playing with. The baby is seen looking out the window, eagerly waiting for the ball to come close to the window so that he can catch it.

Heading 3: The Importance of the Ball to the Baby
The ball is very important to the baby as it symbolizes a sense of adventure and excitement. The baby is shown to be curious and eager to explore the world around him, and the ball represents a new and exciting experience for him.

Heading 4: Conclusion
In conclusion, the baby in the story "What's in the Mailbox?" wants to catch the ball that was thrown by the children playing outside. The ball represents a sense of adventure and excitement for the baby, and he eagerly waits for it to come close to the window so that he can catch it.