I actually got some lock picks around that age. I was also very mature about it. Just wanted to bring that up, because it's non-trivial to become a felon by using (or even possessing during a different crime) those. The recipients should definitely understand the possible risks and be responsible enough to handle that.
Buy them an expensive professional adult tool of some sort. Like a $1000 microscope, a Moog synthesizer, a FLIR camera, a Stratocaster guitar and Fender amp, a high power computer, an automated milling machine, a good 3D printer, a Black Magic Design Pocket video camera and Macbook, a pottery wheel and kiln, a bulldozer, etc. Something they can grow into and which will be rewarding and improve their life for a very long time. Safety is a concern (especially with bulldozers and kilns!) however providing oversight will make it a shared activity.
I second funtional adult tools. I would say maybe don't get them $1k top of the line stuff. Decent mid-level stuff is great.
Power tools are an excellent idea. They can build things and learn safety (ashame shop class doesn't really exist in many places). I had a "business" selling bird houses that I built using power tools around that age.
It is unlikely that there is a way to avoid obsession and addiction Supply an ipad with a reliable high bandwidth "works anywhere" network connection, lots of memory, lots of processor performance, and Minecraft. Sign her/him up for home schooling. Stockpile food and drink that can be consumed while working on Minecraft. Setup sleeping bag and mattress near the Minecraft site.
Cut a deal with the child that they will check-in once a week and set them free.
Spend time with them doing things you like, which don't bore them too much :)
I wish I would follow my own advice more often.
Ok, this is very geeky, but 2 weeks ago I sat with my oldest and did the first couple of problems from Advent of Code in Python, which he's learning in school. We both really enjoyed it, or at least he said he did.
If your 10 year old likes music and sequencing, the Teenage Engineering set of Pocket Operators are very cool. A set of unique samples combined with a surprisingly powerful sequencer. One of them even has the ability to sample from aux in and then use that sample with the built in sequencer.
