For 45-year-old Demi Moore, having a family with her husband Ashton Kutcher, who is 16 years her junior, was always going to be difficult.

The couple have spent the past two years enjoying a never-ending succession of romantic nights at home together in the hope of having a baby, but they have now switched their attention to adoption.

Although Demi already has three daughters - Rumer, 19, Scout, 16, and Tallulah, 13 - from her marriage to Bruce Willis, and friends describe Ashton as the perfect stepdad, those close to the couple say Ashton wants to experience parenthood from the beginning.

'He is the man of the house but the girls all call him Ashton - and he wants to be someone's dad,' one of his friends reveals.

'I think most guys dream of having children of their own and he understands that for Demi having children biologically just isn't possible anymore.

'He and Demi promised each other if she wasn't pregnant by the time she turned 45 they would look at alternatives.'

According to the friend, the couple have decided they want to adopt a baby boy from somewhere in the US, probably down south.

'They gave some serious thought to adopting from abroad, and Angelina Jolie even spoke to Demi and told her how saving a child from a life of poverty and misery would be the greatest thing imaginable,' the friend reveals.

'But Demi and Ashton aren't looking to make statements about world politics, they just want a child of their own. There are plenty of kids who desperately need good homes right here in the States.'

The couple's decision to adopt marks a happy new beginning in what has been an emotionally draining journey towards having a child together.

'It has been very tough especially for Demi,' one of the actress' friends says. 'They tried on a number of occasions to get pregnant through IVF, but it just wasn't meant to be.

'Demi had a very hard time mentally because being 16 years older she worried Ashton would blame her or that he might start to think about leaving her for someone younger.

'But honestly he was nothing short of perfect, he loves her so much and he was there for her all the time,' the friend adds. 'He told her from day one that this was something they were trying for together and God willing they would get pregnant. But if not then it just meant they were destined for something else.

'Ashton will make a terrific father,' her friend says. 'And Demi knows she's lucky to have a man who has youthful good looks but a wise head on his shoulders.'