Hours of sleep recommended for a 12 year old?

[englishpatient]

And a 6 year old?

According to this hours of sleep for kids 5-12 years is 10-11. DD is nearly 6 and generally has about 11 hours i.e. from around 8pm to 7am.

Thank you very much, Seona. DS (nearly 7) usually has about 10 or 11 but DD (nearly 12) has about 9 on Mondays to Thursdays and I was wondering if this was too little - it seems so!