Julia had her daughter Amy at 35. She'd had difficulties conceiving and knew that her prospects of having another child were slim. 'I'd always wanted a girl and as soon as I had her I felt complete. Initially we felt we should try for another, for Amy's sake. It didn't happen but when my sister had two girls 15 months apart I knew Amy would have a ready-made family.'
Amy is now 6 and like Bo, Julia believes her child is perfectly content without siblings. 'Amy has lots of friends and sees her cousins two or three times a week,' she says. 'Because she gets our undivided attention she's very secure and I think being an only child helps Amy to form deep, special relationships, she's exceptionally close to her grandparents.'
For some people the decision to have just one child is financial. Debbie and Clint both have demanding jobs in computing and have a 19-month-old daughter, Ellen.
Like many people these days they don't have family members who can help with childcare. 'We pay a childminder £750 a month to look after Ellen and couldn't afford to do that twice over,' says Debbie. 'For one of us to give up work is also not an option'.