22 rifle in a backpack? I have an OLD Winchester 22 pump, one thumbscrew& it breaks down, but it's still 24", and I can't imagine that in a kids backpack... So a bit of cynicism from me..
On the other hand, Dad's old S&W 22 nickel plated revolver was so small, it fit pretty hidden in my hand when I was a kid.. But in those days we'd have show n tells! Not today!