My DD loved baking at that age, so aprons, cupcake cases, decorating stuff, kids' recipe book. That kind of thing.
She also loved nature things, so magnifying glass, nature books etc.
There are some kids craft books around, so one about nature crafts would be good, with things like nature collages, weaving on sticks, making "god's eye" decorations etc.
My DD also like making jewellery things too, so some nice beads, cheap pliers, and some jewellery findings would be good too.
Another thing DD liked were these 'stained glass' sun catcher kits. They were quite cheap and consisted on an empty metal frame which are filled with coloured "glass" pieces which are then baked in the oven to melt and fuse onto the frame. The finished object can then been hung in the window as a sun catcher and actually looks quite lovely.
Someone once gave DD a kit which consisted of a plaster "rock" and a little hammer which you use to chip away at the "rock" to reveal the hidden things inside. The one she got was filled with a variety of polished stones and crystals (quartz, amethyst etc) which she could identify using the accompanying booklet. It was an amazing kit, she loved it and it was so exciting slowly seeing a stone appear. I've seen other similar kits containing different things, but the stone one was great as the stones were real, not some plastic replica.
Six is such a lovely age, I'm bound to remember more as the day goes on. Now all I need to do is think of ideas for my soon-to-be 18 year old DD, that is really a challenge!