‘I was very excited to spend my life alone, to never get married, to never have kids,' she recalls. ‘People would be like, “Do you want to hold the baby?” I was one of those who's like, “No, you keep it. ”'

They live in the leafy suburbs of Philadelphia, balancing parenthood with full-time jobs as co-chief-executives of a travel company, writing books about pronatalism, and their non-profit projects (to which they donated 44 per cent of their post-tax income last year). They project an image of accentuated preppiness, dressing in ultra-crisp country club, business casual when photographers visit, and are effusive and open to the press.