I need help identifying a vegetable growing in my garden.?

I originally thought this vegetable was some type of squash, but now I wonder if it's young/unripe pumpkins. They're dark green, smooth and shiny growing on a vine with large, flat leaves and yellow flowers. They're also about the size of a large squash. The leafy part of the plant that they grew on grew fast and far over the last two months, completely overtaking the rest of my garden. Inside they are whitish and have seeds in the center, which actually kind of resemble pumpkin seeds. Is this a young pumpkin or another vegetable I don't recognize?