- Firstly, children’s hands vary enormously. Ten-year old boys will often have hands larger than most adult women. Sometimes even very small children can have hands much bigger than average for their age: an example being a renowned female pianist in Australia who recalls that she could play octaves at the age of 4. As an adult, her hand span is unusually large for a woman.
- Children will normally play repertoire that they can manage at their stage of development, which can include quite virtuosic works but without the large stretches and thick chords favoured by certain composers. They may also omit notes or modify the score if needed.
- As child prodigies will normally be playing the piano for hours a day they are especially prone to developing unhealthy and faulty technique if the keyboard is the wrong size, potentially leading to injury later on.
There is no evidence that regular stretching execises can have any more than a marginal effect on hand span.
To quote Deahl & Wristen (2017): 'Despite anecdotal accounts of individuals who express confidence in the value of stretching exercises or devices, there is no empirical evidence that these exercises or devices can physically extend the reach of the hand. In fact, routines or mechanical appliances of this kind have been implicated in a number of devastating injuries, most famously the case of Robert Schumann. They ought to be viewed with extreme caution and are perhaps best avoided entirely.’
Careful stretching as part of a warm-up routine before practice can. however, be of benefit to pianists.
More information: Stretching exercises - benefits, limitations and dangers
While Alicia De Larrocha and Vladimir Ashkenazy had hand spans smaller than those of many (mostly male) concert pianists, they were much larger than those of a big majority of adult women! https://www.aliciadelarrocha.com/en/content/her-hands
They could both just reach a 10th in their youth, which means their maximum hand span between thumb and fifth finger must have been at least 8.5 inches (21.6 cm). This is more than half an inch (1.2 cm) bigger than a woman with an 'average' span for their gender. Only about 12% of women can play a 10th - many struggle to reach a 9th.
Despite this, Alicia wanted Steinway to make her a keyboard with narrower keys, like they did for Josef Hofmann early last century, but this request was not granted. Ashkenazy now deals with arthritis in his hands. https://www.playbill.com/article/vladimir-ashkenazy-says-he-is-giving-up-piano?fbclid=IwAR3pQ0zQXAZ54xnBwqYybZOpwxWNqqo_AqMdD32RTN9QB-Y08CR7rzgzxi
For more information on pianists' hand spans: Pianists' hand spans vary greatly!
Records of prize winners in the most prestigious international piano competitions show that men significantly outnumber women. For first prize winners the gender difference is even more stark.
This gender disparity can be explained by the significant difference in hand spans between males and females, and the demands of the range of repertoire expected.
You can see the statistics here: Gender differences in major competitions and performing careers
This gender disparity does not occur in Mozart and Bach competitions, where women are much more on a ‘level playing field’ with men.
How many potential world class pianists cannot reach their potential due to having to play on a keyboard that is way too big for their hands and also puts them at risk of injury? It turns out to be more than 85% of women and 25% of men who are disadvantaged by today's conventional keyboard!