If Xiao Zhang had been able to persuade her mother to look after the children, Yangyang and Peipei would have grown up as what China calls left-behind children, those whose parents migrate for work, leaving them in the care of relatives.

The families of migrant workers are generally not entitled to education or healthcare in the big cities, so China has millions of these left behind children.

If mishaps befall the relatives left in charge, or if the parents split up while away, the children all too often end up physically or emotionally neglected.

Aware of these dangers, Changsheng was adamant that one parent must stay at home. But as even Xiao Zhang acknowledges now, she was too often out at work, and the children left to eat junk food from packets or work out for themselves how to cook noodles.

At 11, Yangyang is philosophical about growing up early.

“If I ever have children, I'd want them to understand that it's not easy to make money. I'd teach them to think independently and to realise that children can't rely on their parents for ever,” she says.

Yangyang doesn't lean on her parents much. She never needs help with homework and this summer she's due to “graduate” from primary school, a top student and class prefect. Both parents are proud.

CHANGSHENG: You can't order Yangyang around. She'll dig her heels in. That's why I had problems with her when I first came home. But if you explain clearly why you need her to do something, she'll do exactly what you ask. She just needs to understand the reason why.

XIAO ZHANG: Yangyang has never given me any trouble. I never have to ask her to do her homework. She works hard and she knows how to handle herself.

One of the things I admire most about Yangyang is that she also finds ways to have fun and make the best of things.

She's had very few toys, but as a toddler she gurgled with inexhaustible merriment when her mother knocked pomelo fruits down from the tree.

At three, she teased the piglets. At eight, she and her friends were obsessed by clapping rhymes. And now at 11, she goes down to the new city square to take part in the public dancing on a Friday evening.

It's free and women young and old flock from all over the new city.

“I've always liked dancing,” she says. “Whenever I dance, I feel peaceful.”

Some of her friends go to dance classes, but they cost money. Yangyang's been forced to master her aspirations in an often materialistic society.

“I don't have any precious possessions. I'd like a guitar but mum says it's not necessary for me to learn,” she says.

“Sometimes when I'm with classmates who have guitars I feel jealous. The sound is so beautiful. Sometimes when I see other children with mobile phones, I want one too.

“But I know there are games on it which can distract you from your schoolwork. And it is also bad for your eyes. So it doesn't really matter that I don't have one myself.”

Yangyang has learned early not to ask for what she can't have and to be grateful for what she is given.

When she was eight she told me she wasn't sure she wanted her father to come home permanently because her parents always quarrelled so badly on the phone. But now he is home, Yangyang is pleased.

“We have meals at home and mum and dad get on a lot better,” she explains.

“Their quarrels were always about money, but now we have enough. There was one day when we all went to the park together. I think that was my happiest day ever.

“Normally mum and dad are always busy with work outside and don't have time for us. But that day, they were both free, and they spent a whole day with us in the park. I was so happy that day.”