Babies

A little girl raised her hand during a biology lesson and asked if her grandmother could have a baby. The teacher was a bit surprised at the question but answered that the grandmother was too old to have babies. 

"So what about my mother?" asked the girl. The teacher said that it was possible, but that her mother was probably getting too old to be having babies as well. 

"Well, then could I have a baby?" she wanted to know. 
"Goodness no!" said the teacher, "you are much too young." 

"See!" said a voice from the back of the classroom, "I told YOU you didn't have anything to worry about."