Betsy Bird knows all there is to know about kids and books. She is the New York Public Library's youth collections specialist, she writes a blog hosted by School Library Journal, and has served on the Newbery Medal committee. Now Betsy Bird has written a children's book of her own, Giant Dance Party.   In this rollicking picture book, a group of giants shows up at Lexy's door wanting dance lessons. After some initial hesitation, Lexy is happy to teach them, and her dance classes end with all her students-as well as Lexy herself-overcoming their fears and putting on a boogying performance.   Brandon Dorman, an award-winning artist whose work can be found in The Wizard, and on the covers of Fablehaven and Goosebumps, brings the giants and their dance moves to life with his full-color illustrations.