You should get ping pong balls at a sports shop quite easily. They probably won't roll very easily if decorated though!
Another option may be paper/polystyrene balls that you can get at craft stalls (or on line at shops like fred aldous)
www.fredaldous.co.uk/shop-online/paper-balls.htm
What about decorating fairy cakes by making icing sugar (icing sugar and water) or rolling out pre bought white icing and then using strawberry laces or red icing tubes to do the red cross for england flag?
Can do the same with rich tea biscuits which is cheaper if cost an issue.
White paper plate and use a sponge to print black or blue hexagons to make a football.
Draw a large football shirt shape on A4 paper, photocopy and get them to cut out and decorate/colour. If you want you can introduce the idea of a numbered shirt or even writing their name on it too for older children.
Or if you have some of that felt with paper backing and single whole punches (my old pre school did) then pre cut out white circles and punch holes around endges. Let the children lace the circles together and stuff with newspaper, decorate with felt heaxagon shapes to make look more like footballs.
Face painting, white face with football hexagons added, or small circles just on their cheek. Maybe use a mirror and let them do their own...Maybe not?!
Use a large size cereal box to make a football game. Cut off the front of the box and lay on it's back to leave a tray shape, paint it green inside for the grass, make two goals from smaller boxes, roll up a piece or newspaper for your ball and use your fingers to kick it along.
Wow, just realised that I miss working at play school...