Hi, New! Welcome to ATP.
I agree - by far the most likely problem is not enough light. I see those seedlings stretching and figure that their programming "assumes" that they are shorter than other seedlings around them, and "knows" that they have to grow taller than the competition or die.
I think the weak stems are an "assumption" that the plants around them, shading them, will also support them if they can ever just get their darn leaves above the shade!
Most windows are not bright enough to start seedlinhs in, at least vegetable seedlings. If the window IS bright enough, the seedlings tend to cook when the sun shines in directly, and get too cold at night.
Artificial light is usually needed to start healthy seedlings.
If the light is an old-style "T-12" fluorescent tube, the seedlings almost need to grow right between the tubes to be sure they get enough light. (Cleaning the reflectors and tubes will get you brighter light. Replacing the tubes with newer tubes, high-output T-12s, will help.)
If you're about to buy lights, avoid the old T-12s. They are being phased out rapidly. T-8 tubes and fixtures are pretty inexpensive, though the brightest tubes, T-5s, are a little brighter than T-8s and much more expensive.
