Most every self-respecting bluegill I've come across takes to feed almost immediately, so your situation is odd to me. However, maybe as fingerlings, they were a bit too small for the available feed.

It does help to soak the pellets for at least 5 minutes before feeding. You'll get more 'acceptance' of the feed that way.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."