Do you transplant into a different soil at this point?

Yes, they need to go into a quality soil-less potting mix and there are many different discussions here and a couple of FAQ's about when and how to transplant them and which mixes many use and why.

I prefer one with a good time-release fertilizer in it. There are numerous brands on the market but if you prefer a no-dose or low-dose fert one then yes, you will have to supplement it with extra feedings. How often depends on the type of plant and your growing conditions. Usually no more often than weekly is sufficient.

Dave

fabulous question rjinga! I will be re-potting my seedlings this weekend and I have a seed starter peat mix I can use or mircale grow potting soil. I didn't know which to use.

I just did some repotting last week...and found the soil I bought to seem really "heavy" (for lack of better words)...so I mixed about 1/3 of the seed starter mix into it to make sure that the seedings wouldn't suffer...they seem to be doing well.

I just did some repotting last week as well, for my tomatoes. I didn't have any seed starter mix, but I did have a high quality soil-less mix. It did seem a bit "heavy" so I mixed in some perlite, plus some organic tomato fertilizer. So far, so good. Also, I've been watering them with dilute Chamomile tea. That has always worked great for me in terms of preventing damping off and other fungal problems. (It also helps with germination, I've discovered). Regular black tea also works, but not green tea..