Why do my broccoli seedlings keep going like this?

Hi, Can anyone help me please this is my 2nd batch after First lot went like this. They are fine till First true leaves and then leaves crisp up and die. I thought maybe too warm so they been on a North facing window sill but looks like again they going die? What am i doing wrong.
Thanks

 

Hiya.
It could be any number of things, too much water, too dry an atmosphere, too hot at times. As with most things, I always try to think about what a plants natural situation is, and in this case I would have them outside at every opportunity, only bringing them in when a frost is forecast until you're ready to plant out in a couple/few weeks time. Don't overwater but at the same time don't allow to dry out.

Edit : Probably no need to bring them in on a cold night, just cover them.

 

Looks a bit like scorch.
Not a plant to molly coddle, as Freddy says..
I'd have probably sowed the seed outside.

 

Thanks for the advice i have now resown outside i know its abit late but hopefully These should do better.

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