Yes they are far too heavy, so often kids have content which could be stored in school, unfortunately a lot of primary schools don't have lockers meaning kids have to haul unnecessary content around with them all day.
Tablets would also be a great help for them, use of tablets in primary school would surely cut the weight in bags by at least 50%.
I had a look through our son's school bag last night because it was super heavy. He uses a tablet so not too many books but still his bag weighs a tonne. So inside I found- in addition to tablet and books - 2 bottles of water and a can of 007 deodorant!!!
And about 10 wrappers and a million crumbs!!
Typical boy! Messy and dirty but cares about how he smells to girls!