They sound as though they might be either squash or courgettes, although the first few leaves of each are rounded but the proper leaves are then rough to touch and serrated.
http://www.digginfood.com/page/2/
Are the true leaves evident yet? If you only have two leaves wait for more and then describe them.
Either-way I'd wait another week or so to plant out as if they are squash family they need warm days and nights. They also thrive in very rich soil. When I plant mine out I dig a hole and fill it with neat compost from my cooked compost bin. One plant per square metre max.