This summer, the three children of the old Li's family participated in three sports competitions held in Hangzhou, Kunming and Harbin, namely men's gymnastics, pole vault and marathon. The third child did not participate in the competition held in Hangzhou; the child who won the national championship in the gymnastics did not go to Kunming, and the marathon champion was not his third child. Can you guess which child of Lao Li is the national champion of men's gymnastics? ['Boss.', 'Second child.', 'Third.', 'Unable to judge.']