With a simple clap of hands, an itty-bitty beboppin' baby gets his whole family singing and dancing. Sister's hands snap. Granny sings scat. Uncle soft-shoes--and Baby keeps the groove. Things start to wind down when Mama and Daddy sing blues so sweet. Now a perfectly drowsy baby sleeps deep, deep, deep.      Lisa Wheeler and R. Gregory Christie pair up for a celebration of music, imagination, and big families--but they know that even a jazz baby needs to snooze. Oh yeah.