This may not be what you want ot hear, but the answer to keeping them entertaind for 8 hours a day? another kitten.

I REFUSE to foster one kitten at a time. REFUSE. I need at least two or I lose my sanity. Angel's been with Jen all week... and Flutter's been driving me bonkers. I can't wait to have Angel back so Flutter and Angel can entertain each other, and I can have a break! LOL

Its only going to get more obvious once the baby is born. You'll be so focused on the baby that the time you spend with him now will diminish and he'll be bouncing off the walls.