Hi Kirchner3, you can spend a good 3+ hours visiting the park on the Maryland side and doing a part of the Billy Goat Trail. I like to take snacks, do stops to enjoy the view, and so if you are strictly "hiking" it you could do a good hike in less than 3 hours. It's a beautiful park so I would give myself at least 2 hours.

Yes, there is a National Parks fee, plenty of parking, and a fairly short walk to the falls.

It’s part of the National Park Service so, in that sense, it is a “national park” and NPS passes and discounts apply there. But the NPS refers to it online only as “Great Falls Park,” probably because of its small size.

The park closes at 7:45 pm Check their website

The overlooks are fairly close to each other. I'd say in a stroll, a little over an hour or so. Well worth the time. I'm of the older generation, so a stroll is what I have. Enjoy.

Walk out from visitor center and all the trails we did took us along the rocks and water. The best spot we went was very treacherous with steep decline so if you take that one be real careful but is well worth it. The trails aren't marked like an usual park where you got this one and that one just start hiking out visitor center like I said and you will definitely hit everything you want to see.

Yes!

There is not a playground. But kids would enjoy the visitor center exhibits and the hiking trails. There are many trails that a 4-year-old could do. There is also a large picnic area where you could picnic or barbeque. We saw many people playing yard games. Our 6 year old enjoyed the park.

Yes, the rails are level and the bridges to the view points are fairly even and flat. You child may need to be lifted up at some points to see the Falls.