Generally the pumpkin plants produce male flowers first (especially in large numbers) and female flowers arrives one or two weeks after male flowers. So I would say just watch and nothing to worry yet! The female flowers will develop soon. Usually pumpkin plants produce flowers in 10:1 ratio (male:female).
To encourage lateral branches and increase fruit numbers some people pinch off the main vine tip when the plant is 2 feet long. But I believe it is too late for your plants.

Also please keep in mind that once the female flowers arrives they need honey bees for pollination. If your garden lacks honey bees you can do hand pollination by using soft brush or gently rubbing the male and female flowers.