42 pandas have been born so far this year at two key breeding sites in China.

It's the most ever, the result of long study and expertise ... at the China Conservation and Research Center for the Giant Panda.

Among the new cubs, a total of 36 had their public debut last week ... at the center’s two breeding facilities in Sichuan Province.

The births included 15 sets of twins, which adds a challenge for the staff. Mother pandas can't care for two offspring,

Caregivers have to step in and help. Baby formula for humans, mixed with dog milk provides the needed nutrition.

Pandas start tiny, only 1/900 of their eventual size. Every step of breeding and rearing is a challenge, even as the pandas get bigger.

There are now about 2,300 giant pandas in the world. Until very recently pandas were endangered. Conservation has helped change that.

Giant pandas now have a more favorable status—vulnerable—but still require protection. So the work of the breeding sites will continue to be crucial.