Here are a whole bunch of previous discussions on "leggy seedlings" if you want to read through them.

Primary case is insufficient light. It would be very difficult for just window light to be sufficient as most have discovered.

Second cause is too warm air and soil temperatures after germination. Since you waited for all to germinate, the ones that already had germinated got way too much heat and not enough light because the top was still in place. That is the problem with trying to start several different things in the same tray. Usual advice when that is done is to remove the cover and the heat source and move to intense light source just as soon as the first ones germinate. The rest will still come along if they were going to anyway.

Third cause is over-crowding of seedlings.

Dave

Here is a link that might be useful: Leggy seedling discussions