Hi!
It depends on what your are growing. Please post what they are and then we can help you.

FYI- even if they can be potted up, you would most likely wait till they got their first true leaves.

Keriann~

Spindly plants mean that they are to far from the light. Move them close but not touching you grow lights. soon as the second set of leaves come on re-pot them. Bury them up close to the leaves. This was they will root all along the stem.

Spindly stems can also mean that there's too much bottom heat on the sprouted seeds. Be sure to turn off the heat once the seeds have germinated; they'll be much sturdier and stockier.