No sooner is Jack Powell (Williams) born, than it is announced he has a rare disorder that will make his body age at four time the natural rate. Thus, he grows up as a 10 year old in a 40 year old's body. It also means he will have the body of a senior citizen by the time he graduates - if he lives that long.
The formula for Robin Williams' childish stick wares dangferously thin this time out.
Things kick off in spirited fashion, as Karen Powell (Lane) goes into labour at a Halloween costume party and gives birth extremely prematurely to perfectly-formed baby Jack. It is soon revealed that said infant has a mysterious illness that will cause him to grow at four times the normal rate. Indeed, ten years later, Jack has become a healthy, lively young thing who happens to have all the characteristics of your average 40 year old (hirsuite arms, booming voice, razors in the bathroom etc.), yet still hides in a box-cum-playpen and sleeps in his parents' bed when he has nightmares.
But after a decade of hiding behind twitching curtains, Jack longs for more and is packed off to school where naturally the other kids steer clear, until his added height and strength turn him into a basketball natural and his comrades accept him into their fold.
A smattering of amusing moments ensue, but they never rise beyond overly-lengthy fart scenes and Jack's ability to buy Penthouse despite his tender years. And just when his crush on his teacher (Lopez, providing the film's most charming turn) promises to get interesting, illness is chucked in and things take a turn for the saccharine, culminating in a rather vomit-inducing epilogue.
All this really achieves is to provide a stark reminder of a once great director come terribly unstuck. Again.
This is all worryingly similar to Tom Hanks' classic Big, only substituting uninspired humour and leaden sentimentality for the wit and poignancy that made the former such a success. Williams, while occasionally touching, seems to be going through the motions, his peculiarly overgrown man-child unconvincing even with the greatest suspension of disbelief.