Baby-Sitters on Board! (Baby-Sitters Club Super Special, No. 1) By Ann M. Martin Paperback – January 1, 1991
Book 1 of 15: Baby-Sitters Club Super Special
 
Kristy, Mary Anne, Stacey, Claudia and Dawn are the luckiest baby-sitters in the world. This summer they're going on the greatest trip ever: a plane ride to Florida, a boat trip around the Bahamas, and then three days of fun - in Disney World!

Of course they have a million adventures. Claudia gets notes from a mysterious "Secret Admirer." Kristy, Mary Anne, and Stacey make some unusual new friends. Dawn has her first real romance. And they still have time for what they like best of all - baby-sitting.
 
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