APEX, N.C. — There is something about children and boxes. Whether it is making a house or a fort, the bigger the boxes, the more fun they are to play with. Who would have imagined that the boxes could be dangerous?

One mother knows firsthand.

Playful and carefree is how life is for 2-year-old Cassie Bolton. Sherry Bolton said her daughter is a lot like her older sister, Hannah.

Both children loved to play with a "playhouse" Bolton's husband made from a cardboard printer box. Hannah was in it all the time.

"She'd make Cassie laugh hysterically by looking out the windows and, you know, [play] peek-a-boo, going in and out. Hannah'd be giggling hysterically and Cassie would be giggling," Bolton said.

The laughs stopped on a December day in 2002.

Hannah and Cassie were playing in the box while their mother was down the hall doing laundry. Cassie came out and Bolton went to check on Hannah.

"Her legs were sticking out and it was all -- very quickly I thought, you know, she kind of looks a funny color. So I went over and thought I was trying to wake her up. I had to kind of unwedge her head from the window and I couldn't feel her breathing or anything," she said.

Bolton called 911. Paramedics and doctors could not revive Hannah.

"That was really the first instant that I realized she was gone and was not coming back," Bolton said.

Hannah had somehow gotten her head caught between the window and the flaps. In her struggle to get out, the box fell over and Hannah was strangled.

Bolton wants to make sure what happened to Hannah does not happen to any other child. She wants parents to take a second look at things that seem harmless.

"I'm not, like, saying no kid should ever play in a cardboard box," she said."[But] if it saves one kid from getting hurt, let alone, you know, dying, then it's worth me talking about it."

Hannah died less than two weeks before her fourth birthday.

In her memory, the Cary Family YMCA started "Hannah's Fund." Money raised pays for preschool and swim lessons for families who cannot afford them.