I have used the needle guard from Sew-Classic and appreciated having it. If nothing else, it gives a sense of security to the parents!
I have worked with children one on one and also where they have a partner. We go over and over practicing the "stop" procedure. When anyone on the team says "stop", everyone stops. Sometimes the teammate is turning the wheel by hand. We do plenty of hand turning before using the pedal. A child NEVER runs the foot pedal for someone else, but I do with a child on my lap.
With ironing, I hold the iron, and the child moves the fabric, sometimes with me holding her hand. I think the iron is more dangerous than the sewing machine.
I also go over the situation with pins. I ask them ahead of time if they are willing to accidentally get stuck with a pin or needle now and then. We talk about how brave we are and that nobody has any business sewing if they aren't willing to have a pin stick them once in a while.