You can't let the actions of a tiny minority dictate the actions of the majority.
There is absolutely nothing wrong with martial arts instructors of all ages and both sexes teaching classes. The key is in all parties involved protecting themselves.
- instructors with CRB checks and insurance
- a venue and operating practices ensuring that children have a safe environment to train.
- parents observing classes. Watching from the sidelines. never leaving young children alone and asking all of the relevant questions of the instructor and the organisation.
Predators are evil, manipulative and adept at deception. You won't eradicate them entirely, not ever. BUT you can close off their opportunities and make it so difficult they don't even try.