K.N.
My daughter is a junior at Gettysburg College -- she fell in love with it the first time on a family trip there when she was around 11 and our youngest was around 8.
My husband is a huge history buff and it's an interest I share so touring the battlefield was important to us. The first time, we bought the CDs and did it our selves. Although my husband loved it, it was too long and too dry for the kids. Our second trip, we signed up for various ranger-guided tours. These each lasted, like, an hour or two I think and each one focused on a separate part or day of the battle. We did do some traipsing across the fields. There was one that would be a little too much hiking for a 6-yo but the other two really weren't too difficult at all. The rangers offered so much insight and were obviously so knowledgeable and passionate about their topic we all really enjoyed it -- even the 8 yo.
You can drive around the battlefield & stop where you'd like. In addition to Devil's Den, both Little Round Top & Big Round Top are good, get-out-&-run-around places for the kids & offer good viewing sites as well. Oh, and by all means spend some time at the National Park Visitor Center and the Cyclorama. Definitely worth it!
If you want, a great book for you & your husband to read before your trip is a novel called "Killer Angels." It's a terrific read and historically accurate. Perhaps your librarian could recommend a book for the younger kids to read before the trip. If they're aware of the Civil War it will make the trip much more real to them.
In addition to touring the battlefields, there are a bunch of things to do around Gettysburg. Although we've never done one, a number of people really enjoy the ghost tours through Gettysburg (town, not battlefields). Yes, there are several ice cream parlors -- and a couple of cupcake bakeries, too. Check out the Majestic Theater. Sometimes there are classic movies; other times there might be some play or music performance. My daughter also said you might want to check out the train museum or the horse & carriage rides.
If you're looking for casual places to eat, Lincoln Diner is right near the center of town (& across the street from the theater). It's fine for typical diner-type food. Montezuma's is a decent Mexican restaurant; the food's good, inexpensive & quick (though it doesn't have a liquor license, if you or your husband are looking for an adult beverage). The Avenue is our favorite spot for breakfast. My daughter also says The Blue & Grey is a decent place to eat, though I've not been. If you're looking for a nice restaurant (like, linens on the table & more upscale food), The Dobbin House is good -- but spendy. I hear the tavern there is more casual & less expensive but with good food also. I was not a huge fan of the Farnsworth House -- even with a reservation we had to wait forever for just adequate food.
As for places to stay, we like the Gettysburg Hotel. It's very convenient for us since it's right in the center of town & right down the street from the college, though we've not been there since their recent renovation. By the way, the restaurants there aren't bad. We've also stayed at Country Inn & Suites, Federal Pointe Inn and a couple of other places. I've always wanted to try a B&B but haven't found one that fits the budget.
I hope you have a wonderful time. PM me if you have any questions.