Try to answer this riddle. Imade it up I KNOW THE ANSWER?

Yao Ming is driving a bus that has 4 boys, 12 babies, & 7 girls. Yao Ming stops at San Diego. 3 boys get on & 2 boys get off. 9 girls get off & 2 girls get on. All of the babies stay on except 1. How many peple are on the bus ???????????