Dear Economist,

I am writing for childcare advice. I have two daughters, aged three and six months. The younger child sleeps in bed with us, the older child in her own room.

Since the new baby arrived, the older child hasn’t been sleeping well. I am worried that she may be suffering from some sort of sibling anxiety. It causes us problems too, because when she wakes up she walks to our bedroom and often wakes up her sister. Should we be consulting a child psychologist?

Yours sincerely,

T. Monks, London

Dear Mr Monks,

It seems to me that the psychology is abundantly clear. Your older daughter is not anxious, she is responding rationally to incentives.

Before the baby was born, you could afford to ignore night-time shrieks from the toddler, or unceremoniously bundle her back to bed. This would have made waking in the night a fruitless experience for her, and no doubt she found the costs outweighed the benefits and learned to put herself back to sleep.

The new baby has changed the incentives. Your older daughter has acquired a powerful bargaining chip: she can wake her baby sister whenever she wants. In order to prevent this disaster scenario, you respond quickly to any night-time whimpering. The little imp only has to click her fingers to get instant attention. Small wonder she often chooses to exercise that option.

You could try to change the balance of costs and benefits. Chocolate bribes for a night’s sleep might work, or you could bundle the two of them in a room together for a few nights and wear earplugs.

But there are no easy answers: you have weakened your own negotiating position and you will have to live, however blearily, with the consequences.

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