how larger are your babies? Im getting at are they too small to eat a full feeder yet? How many do you have? If you have one maybe two then they may not have any kind of urgency to eat it up right away. In the wild its eat or get left out and when one gets something they all swarm in like monsters to get a bite, VERY jealous fish.
Also are you just sitting there watching them? RB;s are very bashfull and dont like to be watched to much.. Try shutting the lights off and standing back when its time to eat, they should put on a better show. Give them some time.