[SusieB]

My sprouts are the size of marrowfat peas - well the larger ones are.  Is that it or will the later varieties put on some weight?

[mumofstig]

I find that later varieties,  grow and will be ready............................................... later 

[azubah]

I have had small sprouts for years and envied my neighbour's normal sized ones.
Last year I dug in loads of muck and put lime in every hole when I planted my sprouts and they are large this year.
I had F1 seed, as I always do, but it is soil fertility that makes the difference.
I hope that yours get bigger, there is nothing to lose by waiting and hoping.