"The Difference Between..." joke

One day a little boy and a little girl are outside playing together and they get into an argument.
The little boy holds up an army man and says " I bet you don't have one of these!"
The little girl finds her army man and holds it up "Yes I do!" she says in a superior tone.
The little boy looks through his toys and holds up a dump truck and says "Well I bet you don't have one of these!"
Once again the little girl looks through her toys and finds a dump truck and holds it up and says "Oh yes I do!" in a superior tone.
The little boy is starting to get mad so he looks through his toys and finally finds a cap gun. He holds it up and yells "Well I bet you don't have one of these!"
The little girl finds her cap gun and holds it up "Oh yes I do!" in a very snooty voice.
At this point the little boy has had it so he stands up and whips his pants down to his knees and points to his crotch and proclaims "Well I know you don't have one of these!!"
The little girl gets up looks down the front of her pants and then runs home crying.
The next day the little boy and little girl are playing again and once again they go through the routine with the army man, the dump truck and the cap gun.
The little boy jumps up with a big smile on his face and whips his pants down to his kness points and his crotch and says "Well I know you don't have one of these, SO THERE!"
The little girl immediatley jumps up pulls her pants down and points at her crotch and says "Well I might not have one of those, but my mommy told me that with one of these I can get one of those anytime I want one!!"