Reporting
This happens more than most
This happens more than most people realize, and, yes, they will take over the front lawn. Pumpkins send out sprawling vines. (A less on in "be careful what you wish for.") To thin the plants, pull out the weakest and leave the strongest. Cutting back the vines dramatically could effect the growth of the plant and any pumpkins, although cutting (or mowing) off the tips of the vines is not likely to have an effect.