D.H.
Have you tried Party City, or the Dollar Stores? Big Lots? Lots of times you can find those type of things at those places............
If you are going to make it from home, go to Michaels and get their card stock.....they are better than most, for cheap paper......then make the invites.....for decor, you should be able to find soccer stuff, if you have to buy it with a boy on it and put a pic of her over the boy, or cover it up with something....
Good Luck and take care.