* Jane Banks is likely the oldest, appearing to be about 10-12 years old. She's more mature than her brother, often acting as the responsible one and taking care of her siblings.
* Michael Banks is the middle child, likely between 7-9 years old. He's full of energy and mischief, getting into trouble but also capable of moments of sweetness and kindness.
* The twins, John and Barbara, are the youngest. They are probably 4-6 years old and still very much dependent on adults.
Ultimately, their specific ages are less important than their personalities and the role they play in the story. They represent different stages of childhood, and their interactions with Mary Poppins help them learn valuable life lessons about responsibility, kindness, and imagination.