This is also lower than in mid-2011, when 18.1% of the population were aged 0 to 15 years old (around 556,000 children and young people).
Mae hyn hefyd yn is nag yng nghanol 2011, pan oedd 18.1% o'r boblogaeth yn 0 i 15 oed (tua 556,000 o blant a phobl ifanc).