Forget Kate Middleton, this baby news is giant. The panda twins born at Zoo Atlanta Monday were judged to be healthy, of good size, and as attractive as a pair of hairless pink mammals can be.

Both, however, are tiny. The larger of the two is 4.6 ounces; the smaller is 3 ounces. But the twins were doing well Tuesday, with the help of mother Lun Lun’s excellent instincts and a little extra TLC from the zoo staff.

While Lun Lun cared for one twin, curators warmed and tended to the other, switching them out at regular intervals. But it hasn’t been easy. According to a note from Rebecca Snyder, curator of mammals, “Lun Lun is such a good mom, though, that she is reluctant to give up whichever cub she has. So, we have not been able to swap the cubs as frequently as we would like. Because of that, both have been supplemented with some formula.”

Zoo officials warn that mortality among panda infants is high in the first few months, and twins are particularly susceptible, being smaller than the average bear cub. Lun Lun, a 15-year-old giant panda, gave birth at 6:21 and 6:23 p.m. Monday. The cubs are the first giant pandas born in the U.S. this year, and the first pair of twin pandas born in this country since 1987.

Panda twins occur frequently in the wild, but because the mother typically cares for only one, it is rare that both survive.

The twins join three male siblings, all the offspring of Lun Lun, who gave birth to Mei Lan in 2006, Xi Lan in 2008 and Po in 2010.

Mei Lan was at first judged to be a female, but in an ursine version of “The Crying Game” she was discovered to be a male when she was sent to the Chengdu Research Center in China. While Xi Lan and Po remain in Atlanta, eventually all the cubs will relocate to China.