What's your goal here? Are you trying to make it so that their kids can play? Or are you trying to convince them that there is no threat?
I've been playing RPGs for over 30 years now, and I've been an "RPG ambassador" on multiple occasions. So I'm not speaking theoretically here, I'm speaking from experience.
If you're trying to change their minds, don't bother. It's not going to happen. You can argue all you like - you can explain the differences between players and characters, you can make analogies showing that D&D doesn't teach magic any more than it teaches fencing, you can talk yourself hoarse, and it's not going to make any difference. Trust me. I've tried it all.
But if your goal is to create a situation where their kids are allowed to play, the answer is probably simple:
Try a different game.
If D&D (or magic, or fantasy elements) is a trigger for parental fears, abandon it. D&D isn't the only or the best game out there. You don't need magic for a fun game.
Tell the concerned parents (I can't help you with people so nosy that they care what OTHER people's kids are playing) that you are sensitive to their concerns and you don't have any desire to argue with them about what's appropriate for their children.
Tell them that role-playing games are a fun, imaginative pastime that involves social interaction, math, reading, problem-solving skills and more; and that magic doesn't have to be a part of it at all if that bothers them. Then offer them a wide selection of magic-free genres, like the following:
And anything else you can think of. Then pick a game to run and invite the parents to play, or at least to stick around and watch. They might be bored, but they won't be threatened or fearful any more. Be open, honest, polite, mature, sensitive, calm, and reasonable.
You can't convince everyone. But you'll convince more with concern and communication than you will with defensive arguments or anger. Try to remember that no matter how silly the "threat" of RPGs may seem to you, these people are genuinely concerned for their kids.