Thanks all, bit more info or explanation:

I could only get B/F (standard) rewards on the return leg so I put my kids on the reward tickets ( boys under 10)

I did this because I still wanted to get eqm's for my ticket ( I'm the only elite family member)

I thought I could just swap with him, only thing is, they will know I'm not 6 years old!

The big worry now is if they don't let us swap, the kids won't want to sit without their mum or dad!

I offered to put my wife up front but she refused, she's only 5'2" and says she's quite comfortable in the back (strange woman!!)