I'm from Okaloosa. OSCO has mobilized helicopters, bloodhounds, drones and search parties and set up a command post on a bridge in the area. Based on Facebook posts, it sounds like the family and a friend of one of the kids went down to Blackwater River (a very nice, well-used river that is part of a state park) to swim from one of the campsites, and the kids were in their swimsuits when the mom took them to the top of a hill to get better cell service, which is spotty in that area. However, it seems like the mom's cell phone is turned off at this point or out of power. The girl who was with them that is a friend also had a cell phone, which was left in the car.
It is a heavily wooded area, except for where there are campsites, boat launches, etc., but the river has a number of sandy beach areas. It is pretty well used this time of year, so I would think there would be a number of people around. Yes, it is remote in a sense, but it isn't like the middle of nowhere. There are facilities and campsites, etc. and people live in the vicinity.