Birdsall's first book was published when she was 54. The Penderwicks: A Summer Tale of Four Sisters, Two Rabbits, and a Very Interesting Boy introduced the Penderwick sisters and won the 2005 National Book Award.
"The Penderwicks: A Summer Tale of Four Sisters, Two Rabbits, and a Very Interesting Boy" is Birdsall's debut novel, which earned her the 2005 National Book Award when she was 54 years old.