I have four piggies, two about 5-6 months old, and two 2-3 months old. The older ones sit still when I put my hands in the cage, but the little ones FREAK OUT. I usually scratch the older ones behind the ears a little when I'm around ^.^ I think they've figured out that I'm the one that gives them food, and I won't hurt them. THat's not to say they like being picked up - they hate it! They'll let me handle them and pet them, but once they figure out I'm trying to pick them up, they dart to the nearest hidey house XD The little ones can't stand it though - I can't tell if they're genuinely afraid of me, or if they're trying to play. If I BARELY touch my baby's back (like, lightly brush her fur with my hand), she'll popcorn and run away. It's adorable XD
Anyways. It may just be that they aren't used to you yet. I gave mine about a week to get used to sounds, smells, etc., but then I started handling them. Age might have something to do with it, because of the two older ones, I handled Pumpkin a lot, and Ginger very little because she used to bite. Then one day, miraculously, Ginger didn't freak out when I tried to pet her in the cage, and she didn't bite when I held her.
Who knows! Give them time to figure out that your hand = food provider.