Jon Hamm felt ''a little bit left behind'' when all his friends started having children.

The actor and his partner Jennifer Westfeldt have been together for 15 years but remain childless and unmarried, which provided the starting point for their film 'Friends With Kids', which she wrote and directed and they both starred in.

Jon told the Daily Mail newspaper: ''Our friends started having babies and everything became so kid-centric.

''You feel a little bit left behind and you think, 'Oh s**t. Are we doing something wrong?' That was how it started.

''Then Jen wrote a great script that happened to be really funny, very real and yet heartbreaking.

''We saw what was happening with our friends, from feeling outside that because you don't have as much in Common.''

Jon, 41, plays a harrassed dad in the film, and although he's not ruled out having children with Jennifer, he says he was relieved when he could finish The Days filming and give the children he was working with back over to their parents.

He added: ''I'm a big fan of other people's children -- I think they're awesome. What I like about other people's children is giving them back.''

Jon also picked up some tips on how best to handle children, and keep them amused, which would come in handy if he ever does become a father.

He added: ''The most important thing I learnt about kids is how to shut them up by handing them a mobile with the Angry Birds game. It was unbelievable!''