PIF,

Patience is the key to socializing feral kittens. From the pictures, all I can see are EYES!!!!! But I estimate them to be about 12 weeks old.

Put a nightlight in the room and a radio playing soft, classical music. When you go into the room, don't make eye contact as that is taken as a threat. Spend sometime with them by sitting on the floor, tossing them treats inside the cage. Softly talk to them, whispering telling that it's okay. Do this alot. This will get them used to you.

You did a good thing taking in those babies. Shame on the vet for putting mom down. It was not necessary.

Keep us posted. Let me know a little more about them so I can give you other hints on socializing them.