Papu & Bablu

There is a classroom of some small children (5-7yrs), with a genius boy (Bablu) and a smart one (Pappu).The dialogue between the wo and the teacher goes something like this:

Bablu: ""Teacher, teacher! Is Bus male or female?
Teacher: Thinking.......
Pappu: ""Teacher, teacher! It is female""
Bablu: ""Kyon?""
Pappu: ""Kyon ki sab log uspe chadte hain.""
Teacher is pareshan. While Bablu gets in doubt.
Bablu: ""Agar bus female hai aur sab uspe chadte hain to uske bacche
kyon nahin hote?""
Teacher is more pareshan.
Pappu: ""Kyon ki sab us par peeche se chadte hain.""
Teacher is now hiding her face. Bablu gets into another doubt.
Bablu: ""Maana sabhi peeche se chadte hain, but driver aur conductor
to aagay se chadte hain. Phir bachche kyon nahin hote?""
Teacher is sweating as it is getting too much to handle.
Pappu replies: ""Kyon ki woh dono topi pehanke chadte hain.""
Teacher faints !!!!!!!