Is it safe to use lithium-powered devices (open case) with children? I'd like to use this at schools and clubs but I'm concerned about the open case lithium battery solution.

Software Version Problem.
None of the examples in the tutorials work out of the box. If you download the Tutorials and load the files into the current version of Microsoft Makecode they will not compile or download. The issue is that DFRobot has not maintained correct version control or configuration management. Version control applies to firmware (Maqueen, HuskyLens and microbit) and the Makecode IDE. You need to enter all of the code manually from the diagrams into Makecode and when you select Maqueen extension notice you get a different version. There is nothing to identify this except that some of the commands are different. DFRobot should maintain its software.

Sounds good. I actually bought a protected Li-ion battery for it just in case (made by Nitecore). It didn't fit in because protected batteries are longer, so I squeezed the Maqueen's + and - pins with tools. Now it works fine and the battery is surely safe to use.