The three babies cardinals are thriving. I'd estimate they've tripled in size, if not more. Here's a picture of Daddy Bird and the growing babies at 3 days old, then at 6 days old.
Above, a fine looking Daddy Cardinal.
Above, they are 3 days old, they are finally audibly chirping.
Above, at 6 days old, you can tell their eyes are beginning to open. The one on the far left hasn't yet swallowed the little green bug that mommy bird just poked in it's mouth.
More on the nesting habits of Cardinals HERE