Is this a violation of the multi-boxing rule?

[loramin]

Yes, technically.

In practice, no, because no one would notice and petition ... but then you'd get used to doing little things like that, until one day you did something not so little, and got away with it, and then you'd do that again ... and eventually you would get caught and lose both you and your son's account.

I'd suggest it's better to draw a mental line and never cross it, but it's your accounts.