I know this isn't what you asked: but I hope this helps. I ran this with 4 Potter experts, I am not. Here's what I did.
The beauty of PbtA games is the agency it gives the players. Before you start, ask each one of them what three things they'd like to see in the game from the HP world. Start on the train to school and just have them encounter one of those things. They will take the story from there. You'll be there to pepper in the other wishes & help guide their mess of ideas. :)
Yes, this is not what I asked, but thank you anyway. Your suggestion is brilliant because the girls are Potter experts, but RPG newbies. If any of them finds this 'trick' a little bit obvious, I will explain that this is thought as an introduction for them. Just play along with it.
Besides, if you can share your adventure, in any format and level of detail, that will help me. :-)
I wish I could. I started on the train, as one player wanted to do. I asked one of them something along the lines of "as you walk to the back of the train which teacher do you go out of the way to avoid, and why?' this had that player talk about their potions professor whose class they failed. they hide from them, no big deal.
I introduced some house-elves acting sneaky and up to something. they were working for, yup, that potions professor from earlier.
none of it was planned and I've forgotten most of it.
Maybe dig around for some Potter fan-fiction?
