I think we should strive for not repeating the Microsoft situation with a different brand. Like someone else commented, a Raspberry Pi seems like a better solution. Chromebooks are extremely tied to Google services.
I agree with your last sentence though. One single device tied to a single OS is a bad choice. I'd rather give them a laptop that dual-boots Linux and Windows. That at least gives children a taste of the real world where more than one OS is used and learns them how to use both.