1. No internet access 2. A tablet with a few select apps and no games. 3. A tv with a Raspberry Pi running xbmc with a few videos I've curated.
Access to the tablet and tv are limited to certain times, say when we're driving or when my wife's cooking. At some point I'll probably use a PiHole or something like that to give them whitelisted access to a few sites. Not sure where I'll go after that. I don't plan to secretly monitor any conversations but I think I'll stress that I don't consider online and messaging communications to be private and they will be monitored.
As for the money, I'd address the goals separately. Have investment accounts which aren't touched and a performance-based allowance which they can spend completely. I think the Dave Ramsey "when the money's gone it's gone" lesson is something that's supremely important to learn early. And if they need some more money they can always make an appeal to the local VC (you).