How big should my pumpkins be??

I sowed them  at the end of april, they are a trailing variety called Mars F1. Plants have grown well, lots of flower buds, none have opened yet. On one plant there is the begining of a single fruit, about marble sized.

First time i've grown pumpkin, I've been harvesting my courgettes for a couple of weeks now.

Are they doing what they should be doing? 

mine are about the size of tennis balls and filling out fast! 

Lots of flowers on mine but no fruit yet

mine are about the size of tennis balls and filling out fast! 

Same here, my first year so I don't know how, I haven't done anything other than plant.
So far I have around half a dozen but I haven't done anything with the male or female flowers as I'm not sure which is which. The variety is New England which I believe is a small variety, though It's hard to believe with the way the thing is spreading    .

 
mine's trailing about 8 feet along the ground, plenty of male flowers and one solitary ping pong ball at the very end.
 

I have 10 fruit the size of a tennis ball on my 1 plant and they are growing fast.

Do you think this is two many for one plant ?

I have an Atlantic Giant plant with two pumpkins on, one is the size of those big bouncy balls that kids sit on and the other is basket ball size. I'm  in competition with a fellow allotmenteer to see who can get the biggist pumpkin. I seem to be winning at the moment, but there is a long way to go yet! The feeding programe is top secret and there is alot of spying through the hedge going on!. And I'm sure I saw the other grower using a pair of binoculars yesterday. It's getting a bit like the black tulip!
So all you lovely people out there, join hands now and send huge energy messages straight to my pumpkin!.   Thank you!