'You know I have an attitude problem,' says the 10-year-old. There's a hint of pride in her voice.
'Yes,' I reply warily.
'Well everyone in Year 5 and 6 has one too. It's something you get when you're ten.'
Impertinence, I realise, is the latest playground must-have, along with a Juicy Couture school bag, Ralph Lauren underpants and an iPod Touch. Anyone with dreams of status has rehearsed the curled lip and the cocked hip with which to repulse all adult utterances. They've mugged up on fashionable conversation openers: 'You're dead, Mum!'/ 'You just don't geddit!'/'You wanna ruin my life!'. They've jettisoned puerile pleasures: bedtime stories/family time and devoted themselves to the things that really matter: self-adhesive nail extensions, New Look fashions, Jesse J and Instagram.
The shadowed eyes, for which I've blamed hormones, are down to the strain of this transition. I've been distracted by my own frustrations as I watch my little girl changing. Now it dawns on me that she is equally unnerved. Peer pressure is precipitating her into a new world before biology has quite caught up.
At night, freed from other ten-year-olds' eyes, she clutches her toy elephant and asks for a Mr Man story. 'At secondary school I suppose I'll have to invent a new me again,' she says. 'And the trouble is I'm worried I won't know who 'me' is any more.'
Middle-age, I realise, is a blessing.