The rucksack is very versatile.....
We got each of my daughters a rucksack that they started using at age 5 for portaging. They still use them now and my older daughter just did a trip at age 13. Each year I'm able to add more stuff to their pack. At first their pack was very light with just their fun stuff (stuffed animal, coloring stuff, uno, books to read) rain gear, and a couple of other light things. This year my 13 year old carried all of her stuff in her rucksack plus some....... rain gear, water bottle, clothes, camp shoes, sleeping pad, sleeping bag, journal/pens, uno, and some of the camp gear. If you keep it light they can carry the rucksack at an early age and it's a pack that they can continue to use into adulthood.
little duckling at age 5
little duckling at age 7
big duckling at age 9
little duckling at age 9
big duckling at age 11
big duckling at age 13
As you can see in the progression of photos..... the pack doesn't have much in it at age 5 and it gets filled more and more until age 13. On my trip with my 13 year old this year I was able to get so much in her rucksack that we only needed 2 packs for our trip. I carried a ccs guide and she carried the ccs rucksack.