Spring cabbage seedlings

I have some spring cabbage seedlings, they're about 5-6inches tall.  Is there anything I can do with them, or are they too small and too late?  Can I grow them in the greenhouse in big pots, or in little pots to go out in the spring? Or under a cloche outside?
Thanks.

thats exactly the size you want them. plant out and leave them be. give them a feed in spring and watch them go .