Unlike Princess Anne, who liked playing with toys as she posed, the Prince was "fascinated" with the artists and their palettes – and regularly tried to produce his own work.
The insight into the royal siblings' early life has been revealed in the unpublished autobiography of the late portrait painter Margaret Lindsay Williams which has been hidden for more than half a century.
In it the artist, who died in 1960, explains how the Prince and Princess, then four and two, came to her studio a number of times for one of their first ever portraits to be painted.
She explains how they both loved fruit cake and orangeade and how they were "delightful children" who "possessed such strong and individual personalities".
A seasoned professional, she provided dolls and toys for the children to play with but said that the Prince of Wales, who is now a water colour artist, was far more interested in her tubes of paint.