Do you have drain holes in that cup?
I personally would mix up.some new soil with perlite to allow drainage and aeration to the roots and put them in fabric grow bags.
I've never been a fan of see through cups for babies, I think (and so do a lot of others) that roots should be in the dark if you're going to use soil, hydro and aeroponics, not so much.
They'll thank you for giving the roots what they need, most people worry about the leaves, to me if you don't have a stable rooting system you're going to lose in the end.
Good luck.