This sounds like a repeat of the question in this forum a few days ago by a young Lithonian who was being bullied. If your kid wants to learn how to fight back against bullies with a quick learning curve, send him to the local boxing gym. Aikido is simply the wrong thing to learn for him. Once again, another victim of the false propaganda surrounding Aikido.
With all due respect Sir...Perhaps in your Aikido it's considered "false propaganda" to use Aikido to fight back. Either Aikido is Budo and effective against other Martial Arts or it's not...
If this is the case He should go learn something else Why practice something that will only get you hurt?