I'm not an expert and without pictures. if you are using the correct type growing medium, its probably they were on top of the soil or close to it and its just the root hairs on the sprouts thats white and fuzzy. At least thats what some of mine did...

This was just what I thought too---the roots which can run along the surface of the soil and have a disturbing, mold-like appearance.

If you have a picture to share it would be helpful so we can let you know that everything is okay.

Some years back I sowed seeds with a nephew and niece and their Mom, thinking only the best things, threw out the trays so the children wouldn't see 'the mold' which was actually surface roots. Sigh. It's an honest thought that what you are seeing could be mold or a fungus because that's what's it could be imagined to be. But I'm with Crabbcat and think that what you are seeing is the germination and expanding root system along the surface of the soil.

T

Uh oh. I ended up throwing them out. I was afraid it was something horrible and would spread to my other plants. I'm going to plant some more tomorrow and if they come up the same way I'll keep them separate just to see what happens.

Thanks

Good luck with the next set...it's only human to learn from failure, this set is sure to be some of your most memorable tomatoes. I think it's going to be wonderful for you!