If you need the space for something else now, then take them out. Otherwise, you might consider letting them bloom. Brassica flowers attract beneficial wasps. If the variety you planted is open pollinated, you can use the seeds. But if it's a hybrid, you'll need to buy new seeds or plants.

Lisa, you must be chomping at the bit to start your big garden! I've decided to forgo the seed starting process this year, except for direct seeded crops. Instead I will buy seedlings from the local community garden organization. They have a greenhhouse and every spring sell a nice variety of plants, inclding heirlooms that hard to find elsewhere.