The twin giant panda cubs at Zoo Atlanta, the only twins ever to survive in the U.S., are hitting all of their developmental milestones as they approach 100 days since their birth.

Like all giant pandas, they were born nearly hairless, pink, blind and not much larger than a cell phone. Now, they have developed their characteristic black-and-white coats and weigh nearly 30 times their birth weights, tipping the scales at around 7 pounds. Their eyes have opened and they are responding more to their environment and to one another, the zoo said. Plus, the cubs are slowly starting to show off their personalities to keepers.

Click here to see photos the cubs' development from birth to today.

Cute Alert! Watch Twin Panda Cubs Get a Check Up

Since their July 15 birth, the adorable duo has charmed zoo staffers, who have been nursing the pandas around the clock when they are not with their mother, 15-year-old Lun Lun. In the wild, a giant panda mother would typically rear only one offspring at a time, which is why the zoo staff has been swapping the cubs between Lun Lun and a specially designed box.

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The pandas are affectionately known as "Cub A" and "Cub B" until their 100-day birthday, a milestone date in the Chinese tradition, when pandas are named. Five sets of names were provided by the Chengdu Research Base of Giant Panda Breeding in China's Sichuan province, and Zoo Atlanta is teaming up with " Good Morning America" to put it to a public vote, which kicks off Oct. 9.

Watch "GMA" for more panda news and check back here to vote for your names on Oct. 9 on GoodMorningAmerica.com.

As was the case with the cubs' older brothers, Mei Lan, Xi Lan and Po, the names are all Chinese and come from ancient Chinese idioms. Read below for more on the names and check back to vote.

1. Mei Lun and Mei Hua (Pronounced May Loon and May Hwaa) In English, the names mean Lun Lun's twin cubs born in the USA.

2. Mei Lun and Mei Huan (Pronounced May Loon and May Hwaan) These names stem from an ancient Chinese idiom, "Mei Lun Mei Huan," which was used to describe constructed buildings that are tall and magnificent. It has come to mean something indescribably beautiful and magnificent.

3. Tian Lun and Tian Le (Pronounced Tee-an loon and Tee-an luh) These names come from the Chinese idiom, "Tian Lun Zhi Le," which means the joy of family life or family happiness. In this context, the cubs' names would mean, "Lun Lun and her twin cubs are enjoying heavenly gifted family happiness," according to the staff at the Chengdu Research Base of Giant Panda Breeding.

4. Lan Tian and Bi Shui (Pronounced Lan tee-an and Bee Shway) The names, meaning blue sky and clear water, are derived from another the Chinese idiom, "Lan Tian Bi Shui," which is used to describe beautiful scenery.

5. Da Lan and Xiao Lan (Pronounced Dah Lan and Sheow Lan) The literal meaning of these names is bigger one ("Cub B") and smaller one ("Cub A") of the Atlanta-born twins. Watch: First Look Inside Zoo Atlanta's Twin Panda Cubs' Nursery

CLICK HERE to watch Zoo Atlanta's around-the-clock "Panda Cam."

One lucky fan will win a trip to Atlanta to be part of the cubs' 100 Day Naming Celebration at Zoo Atlanta and have an exclusive, behind-the-scenes encounter for two in the giant panda nursery. Click here to find out how to enter the Panda Extravaganza Sweepstakes.