Firstly apologies; I wrote my previous comment in a rush - on my phone - while at work. I haven't thought about this time in my life for a while and I think I was just over excited to share my experience. I shouldn't have gone in with the warnings without knowing you or your experiences. I think want you're wanting to do is brilliant and I truly wish you the best of luck. Your desire to do something off your own back is honestly half the battle and puts you in good standing to succeed.

I will provide some context for why I leapt to concerns because I think it's important to assuage any fears I might've created. I'd appreciate if you could let me know once you've read this comment (or saved it elsewhere if you find it useful) because I'll likely want to delete it afterwards.

I spent the last two years of my time at this company working exclusively in schools and organisations for vulnerable and neuroatypical children, who were no longer attending regular schools. The particular challenges of working with these children are likely not something you'll face, at least not so acutely, and were the reason why I ultimately couldn't continue to do the job. At the time I simply wasn't strong enough to be there for kids that really needed me to be. For most children simply being there is enough, these particular children needed more than I could offer.

On reflection I think the only really important and universal message I'd want to stress on this side of things is don't force them. You might have an idea of how it will go, or what you want them to produce, or even the parts of your sessions that you think will be interesting and fun and they will have other ideas. You have to find the bits they care about, or engage with or are capable of and run with that. This is a skill to learn, both spotting what they respond to and being able to improvise around it. You're still trying teach them something and you have a destination in mind but with something like this that is extra-curricular, you have to flexible about the route you take to get there, and comfortable with idea that you might not reach it, but you can still take them on a journey.

The satisfaction of a child wanting to show you something they've made, that you've taught them how to do, is unmatched. At least I haven't found a feeling equal to it since.

A few more, less philosophical tips;

• An fun and easy way to get some valuable intel on the kids is to have them fill out a printout on day one. I used to use a template I'd created, loosely based on Top Trumps with fields for preferred name, drawing of yourself as a superhero, what super power you would have, what would be your super weakness, and then score yourself out of 5 in a few diverse categories like creativity, friendship, kindness, quick thinking, burping. This gives you an opportunity to identify strengths and weaknesses and a handy way to remember names!
• Kids like big numbers; if you're going to have a number variable, like a score in a game, make it massive, ten thousand points not ten
• Be wary of violence if you're doing games, parents are not all comfortable with it, however crude or cartoony. Make innocuous subs, like water balloons instead of bombs, slingshots instead of guns. Kids will try to get away with it if you give them free-reign of design but make house rules like, "No guns because guns are in loads of games and it's boring, we're trying to do something new!" or "Minecraft is the best selling game ever and there's no guns in that" If you do do weapons make them historic like swords and bows, generally if it's in minecraft it's ok
• If all else fails, toilet humour is always a winner. One of the most successful projects I ever had was a kid who made a fart counter, just a button that incremented a variable and readout at that said "x farts today", I left it on a laptop at the front and the kids would come up and click it when they farted

Lastly, if you want any ongoing advice feel free to come back to me here or I can give you my email address, or if you happen to be London or Cambridge (UK) based, I'd be more than happy to meet up for a coffee. I could also dig try and dig out some of my old Scratch template games and prinouts if you like although no promises I know where that stuff is. Really best of luck with this endeavour, I'm sure you'll have an absolute blast.

In Poland there are quite popular Proton bots. You probably can find them across Europe.

I would use python instead of BASIC, if it was me. I also started with BASIC as a kid, but I remember each step up language wise (BASIC -> Pascal -> C) being a big satisfaction of "hey, it seems like this language is a lot better and I can do more with it." I would echo the recommendation to use actual code though. Language is pretty deeply hard-wired into human beings, and I suspect that the kids that will do well with breaking tasks down into scratch primitives would do equally well with python, and the kids who find python "too hard" or something would also not be able to do too much with scratch. Maybe I am wrong, but that's my guess.

My only other thought is to have some kind of graphical / game you can play / real world robotics angle to it. Maybe there's a little graphical ecosystem pre-provided, and they can write agents that can interact within the ecosystem and then see a visual representation of what everyone's agents are doing. I would definitely recommend to have a bunch of code that they can read, though; that was where my programming as a kid took a big step forward, was when I got a big disk filled with programs I could analyze and break down.

7 Billion Humans and Human Resources Machine (same developer) are probably the most kid friendly ones I've played. TIS-100 I found quite fun, but it's assembly like programming which might be a hard starting point for kids. Zachtronics also make some good games, but the ones I've played are more programming games masquerading as something else E.g. chemistry with SpaceChem.