ABC News' Cathy Becker reports:

When people ask Shellie Tucker if her two toddler daughters, Allison and Amelia, are twins she has only one response.

"I'm like, you have no idea," Tucker told ABC News.

That's because Allison June and Amelia Lee Tucker, now happy and healthy sisters who share crackers and push each other around in a stroller, spent half of their young lives as one, conjoined at the chest and abdomen.

Tucker and her husband, Greg, of Adams, N.Y., were told in November 2011, when Shellie was five-months pregnant, that their daughters were conjoined. An obstetrician who handles high-risk pregnancies told the couple, already parents to a son, Owen, that the girls would likely not be separated successfully and advised them to terminate the pregnancy.

Once-Conjoined Twins Make Debut After Surgery

"As he was telling me, I could literally feel the girls kicking in my belly and I knew that that wasn't something possible," Tucker said.

The Tuckers sought a second opinion at Children's Hospital of Philadelphia, where doctors determined the girls could be separated.

Shellie Tucker continued her pregnancy and gave birth to Allison and Amelia in March 2011.

For the next eight months, the entire family, including then 2-year-old Owen, lived in Children's Hospital with the twins.

Doctors prepared for the surgery by practicing on two dolls sewn together.

"The actual walk-through started with actual baby dolls that didn't really look as cute as the girls but helped us out," pediatric surgeon Dr. Holly Hedrick said at a news conference one month after the surgery.

On Nov. 7 of last year, the team of 40 doctors and nurses conducted an agonizing seven-hour surgery to separate Allison and Amelia, and start the family's new life.

"Seeing them for the first time as two separate girls was really the most amazing feeling," said Greg Tucker.

Today, more than one year since the surgery, Allison and Amelia are thriving as two very individual 2-year-olds.

"Seeing the girls and seeing them climb and get in to things, as aggravated as I get I can't help but laugh because they're an absolute miracle," said Shellie Tucker.

"I'm thankful for every single day," she said. "I can't describe it."