She's not gonna grow 10ins a year, but yes, there will come a time in a few years when she's a fair bit bigger. And maybe then i can put rear pedals on - after all, the seats are gonna be barely any closer together thanks to the lay-back post, it's just the crank and wheel will be further forward. And by then she'll be on her own bike all the time.

I really don't blame your nephew. I wouldn't wanna be pedalling with no steering, either. Being a stoker doesn't appeal at all (being on the front of a tandem isn't all that great, either). But she's been happy sat on the back of my normal bikes as a full passenger for the last couple of years, this will just give us a few more.