Rare conjoined twins who survived surgery to separate them, despite just 2% odds of success, have now graduated kindergarten.

In her 11th week of pregnancy Heather Delaney learned that she was carrying twins connected at the head—known as craniopagus twins—and the girls were born at 30 weeks gestation weighing just 6 pounds combined.

They remained in a neonatal intensive care unit until their first birthday when they underwent a pioneering procedure to separate their skulls at Children's Hospital of Philadelphia, in Pennsylvania.

Although both daughters have developmental difficulties, Abby and Erin are both thriving as they approach their seventh birthday, according to proud parents Heather and Riley, who watched their girls graduate kindergarten this month.

"There are days now where I sit back and think ‘I can't believe how incredibly lucky we are'," said the 33-year-old stay-at-home mom. "Yes, they have disabilities and things they're working through, but they're so happy."

"Watching them graduate, it was like we were dreaming," said Heather who lives in Statesville, North Carolina. "We don't yet know what they can accomplish so the sky is the limit for them."

Baby photos hang in the house of when they were conjoined, and one day the parents will sit them down and "talk about it properly".

"We want them to be proud of who they are and where they've come from."

They go to mainstream school, but attend a special class to get support for their needs. Erin has been walking since she was five, and now Abby is starting to walk too.

"When Abby can run too, I'll be in trouble—it's hard enough chasing one."

"It has always been our goal in sharing our story to try and reach any other parents faced with the same type of pregnancy we were—to give them hope. We want to show there is the possibility they can be separated and then lead healthy and happy lives."

"Now look at them – I'm so proud of them both.

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