Lowes Island is in 20165, Great Falls Forest is in 22066. And, yes, it is Great Falls in Loudoun County. That must be a real blow to would be Fairfax County snobs.

I live in Lowes Island and can walk to Great Falls Forest.
The students do go to Lowes Island Elementary School, at least this year. Always check the boundaries for the next school year to be certain. Great Falls Forest is a very nice neighborhood, about 20 years old, attractive homes, very safe neighborhood. The closest park is Algonkian, which is right on the Potomac, with river access for fishing, boating and kayaking if so inclined. There is also a public golf course there. However, the residents there do not have access to Lowes Island or Cascades pools and other amenities. There is a public pool at Algonkian Park.
Good luck to you in your home search and welcome to Loudoun County!