Are you staying on Canadian side at Niagara falls? Much much better view.

My mother raves about Niagara on the lake. A town close to the falls.

Broad Street Market in Harrisburg PA is a nice place to stop for lunch.

I also recommend stopping by Seneca Falls park. It's really moving. (Especially right now.)

You can drive to Hershey and do Hershey the same day. Spend the night there, then drive to Ithaca (takes about 4 hours). I'm not sure why you're including Ithaca, though, because your current itinerary doesn't leave time to do anything there.

Corning is really fun. If you're planning on doing a craft project there, you might want to go Hershey --> Corning, then stop on your way back to pick up the project so you don't have to pay to have it shipped.

Treman Park, Buttermilk Falls, Taughannock Falls, Ithaca Falls, Sciencenter, Museum of the Earth, Purity Ice Cream, Ithaca Bakery, the farmer's market at Steamboat Landing, Shortstop Deli, boating on Cayuga Lake, the Suspension Bridge over Fall Creek Gorge on the Cornell campus, Finger Lakes wineries such as Sheldrake Point, and more. You could have a great vacation and never leave the Ithaca area!

OP here. This is my tentative plan.

Day 1: Drive from DC to Hershey.
Day 2: Hershey.
Day 3: Drive to Ithaca.
Day 4: Watkins Glen, Taughannock Falls.
Day 5: Drive to Niagra falls and spend night there.
Day 6: Corning glass factory.
Day 7: Drive to DC.

The Sciencecenter is fantastic. I also recommend hiking in Watkins Glen, and visiting Treman State Park. There's a dammed-off swimming hole at Treman by a waterfall, which is gorgeous, and safe for kids (there are several lifeguards on duty and depth changes are clearly roped off).

Is this about driving or about parking yourselves someplace and seeing the sights?

In Ithaca, Homewood Suites means you can stay in separate rooms, but you can't walk to anything; it might be more fun to stay downtown.

Aside from the parks around Ithaca, the big thing to do in Ithaca is the Sciencenter. There's also the Museum of the Earth across the lake.

We plan to see Niagra falls and some state parks near Ithaca, and if we have time cross over the border. We also want to stop over at Hershey or Dutch wonderland on the way there. Any suggestions for where to stay, best route and other things to do. We will be traveling with two kids 5 and 8.