What a WONDERFUL grandparent you are! I'm not sure where to tell you to look for evening entertainment, but I'll bet you'll get lots of answers here.
We like hanging out at the Poly beach in the evenings for the 9PM Electrical Water Pageant on the 7 Seas Lagoon and waiting for Wishes (you get a great view of Wishes with sound from the Poly). What time Wishes shows depends on what time of year you're there. You can grab a tropical drink from the Tambu Lounge or the Barefoot Bar (if it's open) and sip it on the beach. There are hammocks and lounge chairs to relax in.
You could also do a monorail tour of the monorail resorts. You can grab a drink at each one while the kids enjoy the shops and/or arcades or just exploring the resorts.
The Boardwalk is nice at night. There are different kinds of games and street entertainment.
Epcot has IllumiNations at 9PM. Drinks are available just about anywhere.
Downtown Disney has Planet Hollywood and other restaurants, DisneyQuest (I think it's still open) lots of shops to explore.
Hoop-Dee-Doo revue is a very fun dinner show for all ages. Included in the price is all-you-can drink beer, wine and sangria.
Not sure if this addresses your question, but I hope it helps.