My 3 DPs also took a while to understand feeding time. They were as tiny as yours! I had to show them bloodworms for a week before they touched it. Now I'm introducing different foods, but I need to show them many times before they try it! Right now, they all eat snails and bloodworms and one of them eats mussels. I introduced scallop today, they didn't touch it, but showed some interest. I'll be offering it again and I'm pretty sure they'll try it eventualy! They just need training!
Also, just to make sure, your tank being newly set up, did you use a mature filter from another of your tanks to create the biofilter necessary for a cycled aquarium? DPs are very sensitive about amonia, nitrites and nitrates. If your tank wasn't cycled, it might be why they don't eat.