Snow days used to be a huge cause for celebration for kids all over the northern US. Snow days not only meant no school, they meant snowball fights, sledding and building snow forts.

While nowadays we are used to school boards banning activities we always used to do as kids. We grumble about it and say "it was never a problem when I was growing up." Snowball fights are now forbidden, sledding is even more regulated. Sure we used to get some bumps and bruises, but that's no longer a part of growing up.

Making a snow fort seems like a much safer alternative to those activities, but it's actually far more dangerous.

Recently tragedy struck a family in Illinois, as a 12-year-old girl and her friend left church service to play outdoors in the snow. The two constructed a fort, digging deep into the mounds of snow that had accumulated over a wet winter.

When the fort collapsed, the young girls were trapped beneath the crushing weight. Ester Jung was rushed to hospital when she was dug out about an hour later. She was pronounced dead at hospital. She suffocated under an amount of snow most kids would love to jump into.

"It's so sad. It's something she loved to do and she did regularly," said Peg Gradl, a neighbor of the family, to ABC news. "Two little girls just having fun in the snow. It's so normal, but it's a danger we don't often think of."

The 9-year-old who was with Ester was also taken to hospital and treated for hypothermia. She's expected to make a full recovery.

One cubic foot of snow is roughly five pounds, depending on the consistency. If a child digs into about six feet of snow, they could possibly be buried under over 1,000 pounds of snow.

As snow is pushed off of roads and into large mountains in parking lots, it creates a danger that is often tempting to children. On its own, snow is so light, it's hard to appreciate that it can also be incredibly heavy.

There don't appear to be any national numbers collected regarding snow fort or snow bank accidents, but one health official in Canada said that country sees about one suffocation death every year.

The US is ten times the size of its winter neighbor, so the numbers could be much higher.

Winter has its beauty, but it also has its dangers. Make sure your kids know what's safe when it comes to playing outdoors.