No sooner had Vin Diesel established himself as The Next Big Action Hero than he attempts to show us his cuddly side. The mumbling macho man has just signed to star in family comedy The Pacifier (that's The Dummy to you and me, and no pun intended). VD will star as a secret agent whose most perilous mission sees him babysitting the kids of a government scientist. Ah, just thinking about it evokes the smell of soiled nappies...

Unfortunately, this was inevitable. A sappy kid comedy is a must-have credit for any "self-respecting" action hero hoping to reach an audience beyond 15-year-old fanboys and Al Quaeda. But it's a dicey proposition with few movie tough guys escaping unscathed.

Consider The Last Action Hero: Arnold Schwarzenegger. As The Terminator he boasted a body count slightly higher than his IQ (you do the math). And then came Ivan Reitman's Kindergarten Cop. Although the sight of a 6ft bodybuilder peeing into a 1ft high urinal is vaguely amusing, this would lead to the unconscionable Junior (also directed by Reitman). Frankly, the sight of Arnie "with child" was only slightly less appalling than the prospect of a kiddie sleepover at The Neverland Ranch. (Being elected California's favourite baby-kissing politico was the next logical step.)

Then there's Beverly Hills Cop Eddie Murphy, who brazenly flouted that old showbiz adage: never work with children or animals. He was laughing (like a donkey) all the way to the bank after Dr Dolittle, but then came Daddy Day Care - the place where laughter goes to die. Still, enough of you forked out as the sequel, Daddy Day Camp, is now in the works. The downside for Murphy is that he's no longer taken seriously as an action hero. It's not a gripe you hear often but Beverly Hills Cop III, Metro, I-Spy, and Showtime all bombed in a style so spectacular that Jerry Bruckheimer wants to make a movie about it - only he won't hire Eddie Murphy to be in it. Now that's gotta hurt.

And what about Bruce Willis? The Die Hard star may have hit pay dirt opposite Haley Joel Osment in The Sixth Sense, but have you forgotten cosy comedy follow-up The Kid?... Exactly. The Disney flick about a cynical old bald bloke (guess who) finding his inner-child in the form of portly half-pint Spencer Breslin (The Cat In The Hat) made an impression similar to that of a supermodel's backside in a sofa cushion. And let's not even mention Look Who's Talking Too.

Rocky aka Sylvester Stallone made his pitch to the milk-and-cookies crowd in DreamWorks' Antz. Although not a massive hit, the tooner did respectable business - certainly more profitable than anything Stallone has done in over a decade - so when Robert Rodriguez asked Sly to appear in Spy Kids 3D, it was a no-brainer. Unfortunately the third instalment of the Spy Kids franchise made the plot of The Matrix Revolutions seem coherent. After one misfire too many, Sly has returned to the drawing board (i.e. Final Draft screenwriting software) to write himself the starring role in cop story Rampart Scandal (recounting the botched investigation into the deaths of rappers Biggie Smalls and Tupac Shakur).

Apparently the moral of the story is this: learn to be yourself, listen to your parents, do your homework, eat your greens, and drink your milk. Then maybe one day you'll grow up to become an embittered pumped-up steroid case with your very own gun-toting action figure and a polymer-based wife to match. It's The American Dream © Hollywood Studios. All rights reserved.