1.A high proportion of five-year-olds have teeth in poor condition.
2.Finland provides three years of maternity leave and subsidized day care to parents, and preschool for all five-year-olds.
3.Maria Droujkova is a founder of Natural Math, and has taught basic calculus concepts to 5-year-olds.
4.He suggested a link between class size and test results of seven-year-olds.
5.A quarter of 4-year-olds frequently wet the bed.
6.More than a quarter of seven-year-olds cannot add properly.