If I recall correctly I didn’t tell them much about anything. One of them had a nerd dad who set up his daughter with Linux at home but she wasn’t familiar with the install process. I gave them some basic info when I gave them the rules (you have to connect the hard drives and ram) but for the most part everything was new to them.
On the other hand, I also ran a computer club with some other kids (in a younger grade) where we took that pile of broken computers and salvaged working parts. We ended up with 3 or 4 working pcs that we ran Linux mint on. They used the computers for Roblox or something at lunch lol. The computers ended up being a popular attraction at lunch!