I am having problems growing brassica seedlings in my
extension/conservatory (2 big windows ytem 20+

They sprout just fine and grow to an inch and a half/two inches high

Then they stop growing (just as the second set of leaves is emerging),
start falling to an angle and the leaves start to curl up and die and I
am left with a stork at 60 degrees with dead leaves on top of it.

What am I doing wrong?

Thanks in advance