JOPLIN, Mo. (AP) — Triplets born prematurely just five days before a deadly tornado slammed Joplin, Missouri, have started school.

The Joplin Globe reports that the sisters arrived eight weeks early and weighing a combined 6 pounds before the tornado struck in May 2011, killing 161 people.

Addison, Reagan and Lauren Harper had health problems that forced them to remain in the hospital long after their birth. Their family's home was among those destroyed in the tornado. One of the triplets had multiple surgeries for congenital heart disease and has a pacemaker.

But on Thursday, the giggling 6-year-olds piled out of their mother's minivan wearing matching T-shirts that read "Hello, Kindergarten." Their mother, Jayme Harper, says the strength of the girls "amazes" her. She says she is "kind of envious of them because of how strong they are."

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Information from: The Joplin (Mo.) Globe, http://www.joplinglobe.com