Sorry, no it is not normal. Your seedlings are starved for light and as the many discussions here and on the Growing from Seed forum show, it just isn't possible to grow healthy seedlings using only window light. It just isn't intense enough nor full spectrum enough nor long enough exposure this time of year. That is why most all of us use various types of fluorescent light set-ups. This time of year we even have to use supplemental lighting in the commercial greenhouses.

In this case enclosing them in a sort of plastic greenhouse only reduces the light exposure more. I'd suggest a review of the FAQs on the Growing from Seed forum and have linked one on lighting below.

You can try to save some of these (the ones without broken stems) by transplanting them into deep containers (remove the netting first), burying all the stem, and then arrange for much more lights for them or they will just get leggy again. Search 'light set-up' here for many discussions and photos on various seed starting set up.

Hope this helps.

Dave

Here is a link that might be useful: Growing from Seed FAQs