Things that went down well here around the age of 6-10:
crystal trees or crystal growing kit
gyroscope (I still remember getting a gyroscope in my own stocking one year with great fondness)
a compass - perhaps one on a karabiner so that she can attach it to her bag
a whistle that sounds like an owl call
A set of silk “daisies” or “buttercups” that you can make into an artificial daisy chain - NT shops do them
DD very much liked a super-whizzy stunt yo-yo that lit up at that age
A mini kaleidoscope or bug eye viewer
one of those dinosaur egg things that swells up and “hatches” in water
a paper laser
glitter bouncy ball or light up bouncy ball (I got DD a polyhedron rubber bouncy ball from the Tate shop that lit up - that went down well!)
Sunlight photography/contact paper sets (you can get mini kits from the national trust - very stockingable)
a cat’s cradle string and instructions
new skipping rope
harmonica or other small musical instrument like mini wooden pan pipes
one of those ceramic bird callers that you fill with water to use as a bird whistle
a UV light invisible pen set
marbles
game of jacks or travel chess or Ludo or similar
light up flashing bath disco light
a magnet science kit
set mini highlighters
interesting bookmark/s
paper clips in the shape of bicycles, cats and dogs
DD always also gets small notebooks, washi tape, pens, hair things, some kind of bath thing (usually a luxury soap from TK Maxx), and a little cuddly toy of some kind - her favourite was a Mouse in a little house box from Rex London;
One year DD’s absolutely favourite stocking item was one of those multicolour biros with twelve colours that I’d got cheap from Tesco!
For ideas: look at National Trust shops; museum shops; Rex London for great small games and toys; John Lewis pocket money sections.
If I can remember any others I’ll post them! I love doing the stockings and spend all year collecting interesting little things for them. I’m a bit sad that DD is getting older and isn’t as keen on things like this any more 😭