I've done very short presentations for boy scouts. If you're really going to teach first aid, then I'd teach it from the scout book. We found that for an hour presentation that we didn't have enough time to teach a topic properly, so instead used our time a bit differently.
We set up three stations, and had the kids go from station to station in groups. The kids absolutely loved it, and the scout parents thought it was great.
At the first station they learned the very basics of calling 911, how to be a good caller, and how to deal with an emergency. We gave each boy scout a pair of purple nitrile gloves, and told them that we don't touch blood without having on gloves. We then went over the very basics of stopping bleeding (elevation, direct pressure, bandaging). By the time we got to the end of the presentation, it was time to go to the next one.
At the next station the students got to see the inside of an ambulance, got to play with the suction and O2, and the Paramedic explained the LifePak 12 and did an EKG on a student. As a teacher an EMT I wouldn't dare touch a student without an adult nearby. You can place electrodes on exposed skin, or have a student place it himself so you don't have to. The kids loved to see the EKG.
I can't remember the last station, but it was actually put on by the scouts.
I can remember that the kids loved getting a pair of purple nitrile gloves, and we even had parents say that they wore them the next few days at school. Kids also liked the basic ambulance demo.
Even as a sixth grade teacher, I forget how young they are. You want to be very basic and to the point. I'm not sure how much you can do in an hour, but good luck!