One Direction are turning into men.

The 'Little Things' hitmakers - Niall Horan, Liam Payne, Zayn Malik, Louis Tomlinson and Harry Styles - think they have changed a lot since they first found fame when they entered 'The X Factor' as solo artists before Simon Cowell put them in the group in 2010.

Niall said: ''I mean we were all just kids ... You get pushed straight in and have to grow up fast ... We've got bigger, we've got stubble, we're turning into men.

Niall's bandmates agreed with him, saying they thought it was especially hard for them to deal with their early success because they didn't know one another well enough to rely on each other for support.

Zayn said: ''We've all changed. None of us really knew each other and none of us was really prepared.

''I found it hard talking to people, answering questions, but then you realise everyone is in the same boat. You can't take yourself too seriously, and you all start to relax into being who you are.''

The 'Story of My Life' hitmakers admitted that although they're enjoying their success and being able to go on perform at arenas, they often like to relax in their tour bus rather than going out partying.

Liam told Top of the Pops magazine: ''It's pretty hard to just 'go out' ... A lot of the time we actually prefer sleeping on the tour bus. We park outside the venue and just stay there. We have our DVDs and Xboxes and we have a quiet bus for sleeping.''