Place potatoes and sweet potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer just until fork-tender, about 15 minutes. Drain.
Melt butter in a skillet over medium heat. Sprinkle potatoes and sweet potatoes with salt and cook until beginning to brown, about 3 minutes.
Mix in dates, pumpkin seeds, brown sugar, and cinnamon. Cook and stir until dates are warm and pumpkin seeds begin to brown, 1 to 2 minutes. Remove from heat and serve.