We had a very large group (a full house including two toddlers) and this house was great. There was plenty of outdoor seating for everyone for meals, two of the rooms had plenty of space for a pack and play/toddler bed (one has a walk in closet). The beds are *extremely* comfortable. One of the two full baths is ensuite to one room, which is a bit awkward, because considering how many people were staying in the house, more than two people needed to have access to that shower. The decor is lovely but also minimalist, which is great for traveling with small children (very few breakables.) The room with two twin beds doesn't have a door.
The hot tub was lovely and extremely clean. There is also a large backyard which the kids loved running around in. The kitchen is huge (5-6 adults could easily cook at the same time) and was well stocked with basic cooking supplies in good condition and there is a coffee pot in addition to the keurig. I would recommend bringing extra trash bags (and there is recycling at the KOA, but there is only one trash can provided at the house) as well as your own saran wrap and/or storage containers/ziplocks if you'll be cooking. Basic travel toiletries and dish soap were provided, which is always nice. Parking fit 6 cars.
We enjoyed being able to go to the KOA pool and use the facilities. We also were able to walk over to the national park, and with parking in downtown Harper's Ferry being pretty limited, it was nice to be able to just drive to the park and catch the shuttle.