At least they are maples but it is too early to tell what kind

Very possibly. But best to wait for second set of true leaves to tell.

Some of them look very much like several of my first- year seedlings. I'm new at this seedling thing, though-- I agree with gardengal.

It's hard to tell but I don't think so, usually the first pair of leaves has sharp points along the leaf, not rounded edges.

Japanese maple seedlings can be extremely variable in their leaf shape. I wouldn't care to make broad generalities when they are only displaying their first set of true leaves.