What is your set-up? Are the seedlings close to your lights?

When you say thin stems, I immediately think of lights being too far away and the plants stretching themselves into this predictament.

Can you post a pic?

I agree, I think its a lighting issue. Not enough sun. Once you get them outdoors, they will reseed for years, you won't need to start seed indoors unless you want to. I get more reseeded nicotiana then I know what to do with.

I have them in a sunny window(3-4 hours a day normally)and good light for several more, however, we have received very little sunlight(lots of clouds) in the last 2 weeks so that may be the issue as you both suggest. I have no camera currently but they look similar to a pic I have attached from the web minus a couple of leaves. Mine just sit on the soil with a 1/4 - 3/4" thread of a stem below the leaves lying on the soil. The leaves look healthy though.
Thank you

Here is a link that might be useful: {{gwi:233991}}

Also- forgot to ask in previous response.
It was mentioned that they will re-seed for years. Will that even happen in a cold climate such as Ontario, Canada which is a 5a zone?
TY

The pic you posted...that plant looks just fine. This is what your seedlings look like? I remember my nicotiania seedlings were very compact plants, growing low to the soil. Even if your plants were missing a couple of leaves, as you mentioned, I don't see an issue. Although, the sunlight you are giving them is minimal. My seedlings were getting about 14-16 hours of lighting, with bulbs within inches of the plants. When I read your description of your plants, this was what I was expecting (pic on left)....

src{{gwi:233993}}'>
picture courtesy of calgary garden coach

That pic on left is what the stems under my leaves look like. A little shorter but just as weak. The leaves on mine are quite healthy though. Hopefully some good sunny days will strengthen them as suggested.

I have found from trial and error to grow them in the pot or spot that you want them..