I went to the store and got some tiny jars of meaty baby food and some baby spoons.
According to their reactions, it is the BEST TREAT EVER!
Every time I enter the room, unless it is an actual meal time, I give them each a little spoonful of this baby food. This morning, one of them actually approached me. She actually came over to where I was sitting. First time! Of course, she went right back under the bed, but it's another baby step.