No, that's not the correct interpretation. 1/3 of children who are tested test positive. The children who are tested are (probably) ones who are more likely to

No, that's not the correct interpretation. 1/3 of children who are tested test positive. The children who are tested are (probably) ones who are more likely to be showing symptoms or to have been exposed. The rate of infection in the broader population of children is (probably) lower, though it's hard to say by how much without doing testing on a random sample of the population.