* Henry (Benny) Alden: The oldest and most responsible of the children. He's the leader and often takes charge.
* Jessie Alden: The second oldest and the most practical of the children. She's good at cooking and keeping things organized.
* Violet Alden: The middle child and the most imaginative of the children. She loves to read and tell stories.
* Rob Alden: The youngest and the most mischievous of the children. He's always getting into trouble, but he has a good heart.
There are many other recurring characters in the series, including:
* Grandfather Alden: The children's grandfather who is wealthy but doesn't want them to know about his money.
* Mr. and Mrs. Baker: The kindly neighbors who help the children.
* Gertie: The Bakers' daughter who is the same age as Violet.
* The Secret Agent: A recurring antagonist who often gets in the way of the children's plans.
There are also many other characters that appear in specific books in the series.