Sidney, those are very nice-looking cabbage seedlings
Caroline, I wouldn't think you'd have any trouble finding some sort of Bt -- I like the liquid form because you really need to get it on the top and bottom surfaces of the leaves and it seems easier with the spray (for me, anyway). You can also use something like Reemay (floating row cover) or a fine mesh covering to keep the cabbage butterflies away from the plants; if they can't get to the plants to lay eggs, no worms. Next to slugs the cabbage worms are my worst garden problem.