I'm not suggesting that Elizabeth was unintelligent - that remark of hers was highly perceptive (unless she was just trying to play off one parent against the other).
But I think back to when I was seven or eight, and required to write 'news' every Monday morning at school,and could never think of anything interesting to say about going to the supermarket on Saturday morning with my parents or whatever it happened to be. Nowadays, with the benefit of 50 years of life experience and a developed sense of humour, I could produce a nice jokey piece comparing a visit to the supermarket with Prince Harry's expedition to the South Pole.
When I was 10 I did draft a letter for my younger brother to send to the manufacturers of Action Man asking for replacement parts after the dog chewed them up, which was quite unintentionally hilarious. I was furious because I thought 'because our dog chewed the above articles' was very businesslike. But eight is not ten, and I really was intellectually pretty precocious.
Ann