I've gotten a few questions over the past week or two from readers who have noticed white, fuzzy mold growing on their seedlings. This is a fairly common issue for those who start their own plants from seed. The good news: the fungus itself is not going to hurt your seedlings. The bad news: that fungus is a sign that your soil is too wet. Soil that is too wet can result in having the delicate roots of your seedlings rot, which will eventually result in plant death.
Luckily, it's an easy thing to fix. Chances are, you're watering too much. Don't water unless your seedlings really need it -- it's easy to get into a routine of just giving them a quick water every day or so "just to be sure," but this can sometimes do more harm than good. Check the soil's moisture with your finger; only water if the soil is dry.
Another thing that can help the situation is to increase the air flow around your seedlings. You can do this by having a fan running nearby for at least a few hours a day. Not only does this help prohibit fungal growth, but it also results in sturdier seedlings.
You may want to look at how much light the seedlings are getting. They need at least twelve hours of good, strong light per day to grow well.
Finally, if at all possible, consider bottom-watering. This not only encourages the plants' roots to grow deeper, but also helps alleviate mold and fungus because the surface of the soil is not constantly moist.
I hope this helps! If you have a gardening question, feel free to email me at firstname.lastname@example.org -- your question may just inspire a weekly "Reader Question" post!