There aren't many professions where you start as a child and keep doing the same thing for as long as possible. Playing doctors and nurses doesn't count. With rare exceptions, professional sports people don't grow up.
There is a story, possibly apocryphal, about a national team performing some non-sporting duty and being kept waiting. So loudly did they complain that a lackey was sent out to buy them all PlayStations to shut them up. So if you start young, it seems, you stay young.
This alone should make any parent beware.
One of the key performance indicators of a successful childhood is that we leave it behind. The consequence on a psyche of continuing to do in adulthood what you have been doing since the age of 5 or so can only be delayed development and permanent immaturity.
It sounds like fun. After all, you play sport, you don't practise it like a profession or work in it like retail or hospitality. But "play" is probably the wrong word. There is precious little playfulness in any professional tennis match.
There is also an internal contradiction at the heart of sport that must do your head in.
How do you reconcile the rule that "winning isn't everything, it's the only thing" with the unavoidable fact that every time someone wins, someone else loses - one party in team sports, sometimes hundreds in individual pursuits?
For the most part, sport makes losers, not winners.
Professional sports careers, with the exception of darts and billiards, end in early retirement, usually somewhere in your 30s.
Ahead for most are bleak years of readjusting and tedium as they sink into anonymity. The Martin Crowes and David Kirks who go on to forge successful new careers are exceptions rather than the rule.
All the good things about sport cease to apply when you have to win for a living. Team spirit and individual effort for the good of all, which fly in the face of current political orthodoxy, are soon sacrificed to self-interest when continued selection or prize money are at stake.
Those are a few of the downsides.
We haven't even touched on what it must to be like to be judged by thousands of unqualified people every time you do your job; to be a target of verbal abuse from every pub bore who recognises you; to carry constantly the weight of other people's expectations.
Who except the most selfish parent would wish to see this in their child's future?