Off-topic: I was assigned this topic. I guess because @YvesB is also running a CoderDojo. Hi @YvesB, nice to meet you. I run a Dojo in Tilburg, The Netherlands.
Where are you from?
If you are using App Inventor and have some micro:bits or other microcontrollers you could also start using MicroBlocks. MicroBlocks makes it really easy to program microcontrollers in a live environment.
The developer of MicroBlocks made an MicroBlocks extension for App Inventor.
Using that extension it is really easy to program an app that can control a microcontroller. I already made a lot of them. One of them you see below.