I put in a small piece of algae wafer & a small piece of cucumber once some of the babies had used up most of their yolk sac (4 days old). They still don't eat much so I change out the leftover food daily & make sure there is always food available.
You can also put in other veggies if you have them on hand: http://www.bristlenoseworld.com/t69-pleco-veggie-list
Mine are still in the fry saver (plastic kind) & per responses to my intro post: http://www.bristlenoseworld.com/t4790-jumping-in-head-first
they should be fine in there until ~2cm+ big. Although some people do choose to move them to a "grow out tank" it has to be cycled etc.
I plan to just keep mine in the fry saver for a bit and either sell them, bring them to our LFS or let them back into the main tank.