Sunflowers floundering?

I was really touched when Katy gave me this sunflower 'kit' and it was fab to see them all germinating and looking so well. I love sunflowers ... they just make me smile.

Now I feel they may not be doing too well and being a rubbish gardener I don't know what's best. I'm tempted to leave them outside in their smart tub in the hope the slugs and snails don't get them .... or should I plant them out and keep an eagle eye out for the pesky munchers????