Rumer Willis loves the idea of expanding her unconventional family - she wants her mother Demi Moore to have a baby with stepdad Ashton Kutcher.

Demi Moore, 46, who has three daughters with her ex-husband Bruce Willis, wed the funnyman in 2005 and recently admitted she would love to have a child with her younger partner.The star's eldest daughter, Rumer Willis, revels in her new family set-up - and is hopeful her mom will cement her brood by falling pregnant for a fourth time.She says, ''I love the idea. After all, our family continues to grow in so many ways all the time - growing in numbers could be a good thing.And the 21 year old is hoping a future sibling will be a boy - so she and her two younger sisters, Tallulah and Scout, can show him who's boss.