I got a Dell Chromebook for my mother.
It's nigh on unbreakable, and is great for non-tech parents. Each tab/app runs in its own sandbox, and it allows them to do the things they want (i.e. browsing).
It automatically updates in the background (none of that Windows update rubbish), it has inbuilt malware block lists (via Chrome Safe Browsing), it's fast, doesn't bog down over time etc.
Even if by some magic they brick it, a simple Powerwash (https://support.google.com/chromebook/answer/183084?hl=en) and 5 minutes later, it will be back to a pristine state, they log in with their Google account, and it pulls down their settings again.
Also, if you want to see the latest and greatest coming in ChromeOS - try the Canary channel =). (But be prepared for rough edges).
Feel free to ask any questions.