I and my wife have enough SkyMiles to book myself and the kids to Europe. There is availability on the flights we want, but I would need to book one of the tickets for my 13-year from my wife's account. We'd be on the same flight, but he would have his own reservation.

How can I do this with as little hassle as possible? I.e. not having to transfer miles and pay transfer fees nor having to pay unaccompanied minor fees.