The phrase "1 in 3 children have..." is better written "One in three children". This probably applies to all numbers up to ten, except when they refer to doses.
Similarly, with fractions 1/3 should be a third, 1/2 a half or 50%. With fractions outside the range down to a quarter, percentages should be used. The sentence: "Most (80%) of children have..." doesn't need the word Most, or the brackets.
If age greater than sixty years is a risk factor, then write this, not: age > 60y
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