A pair of twin polar bear cubs born at an aquarium in China have celebrated their first 100 days on earth. Born March 5 at Tianjin Haichang Ocean World, the baby bears spent their first days in an incubator, and staff were unsure if they would survive. “They were so tiny at birth. The elder sister was 497 grams and the younger one was 560 grams,” keeper Sun Qinbao told the Daily Mail. But now, the bear cubs are healthy and doing well. They celebrated their “100th-day birthday” by romping around with a ball.