There are three small classes in kindergarten activities. What does this joke mean?

There are three small classes in the kindergarten today. Every class must shout slogans when they come out: the slogan of the first class is: "Primary one, primary one, strive for the first place [Yi tooth] [Yi tooth] The slogan of the second class is:" Xiao er, Xiao er, unique. "[Yi tooth] [Yi tooth] As soon as Class Three appeared, she shouted the slogan:" Little three, little three, dad's heart! [Yi tooth] [Yi tooth], all the dads fainted. . . [giggle] [giggle] [giggle]! Happy Children's Day!