little girl pregnant joke

In a second grade class, a little girl asks, "Teacher, can my Mommy get pregnant?", "How old is your mother, dear?" asks the teacher. "Forty." she replies. "Yes, dear, your mother could get pregnant." The little girl then asks, "Can my big sister get pregnant?" "Well, dear, how old is your sister?" The little girl answers, "Nineteen." "Oh yes, dear, your sister certainly could get pregnant." The little girl then asks, "Can I get pregnant?" "How old are you, dear?" The little girl answers, "I'm seven years old." "No, dear, you can't get pregnant..." Then, the little boy behind the little girl gives her a poke and says, "See, I told you we had nothing to worry about."