Hiya Mirimaran
just thinking about your boys, a couple of years ago Tara was into collecting
bugs and butterflies.
We got her a Bog Barn, I think it was by National Geographic - a great toy with
magnifying panels in the barn, and tweezers and bottles for water for the bugs and a book on what to feed different things you find in the garden - we didn't see her for days, collecting snails, butterflies moths etc.
Another thing that I had as a 12 year old, and you can get toy versions is a microscope- its really fun looking at flys wings, spiders legs and blue bottle eyes and stuff, even liquids can be quite interesting, and a human piece of skin, or a hair.
Most of these are available in Argos, but you may get them at car boots too.
Julie