I think I'm stuck. I found the earrings and a Playmonkey Issue #22 while exploring, but I can't do anything with them. There are no missions for me to do and I can't explore further.
PS - managed to get #5 to start the quest by going to her room at night time while she was there. Is the quest start a random, unmarked event? - It's also weirdly convoluted that you can have them with you before the quest starts and are forced to pretend you don't have them yet.
PPS: Now it seems I can't give her the earrings. Whenever I try, protag just says "I should retrace her steps". I can't explore, she has nothing in the questions, other kids have nothing to tell me about it. The quest shows the first 2 points, "ask about it" and "find it" as complete
Other things I've found: If you give a repeat serum to either girl, the game just cuts back to the room you were in
* After making a serum, if the icon of the backpack is still open in the bottom left, right click (back/menu) doesn't work, you have to click the backpack again.
* If you sell stuff and load the game, whatever you sold will remain on the buyback menu, you can "infinite duplicate" stuff this way
* Exploration seems to wait "24 hours" - if you explore in the late afternoon, you can't explore in the morning of the next day because protag "I have already explored today"
* That questions minigame with #2 and #4 doesn't get saved in the savegame either. If you mess up the choices then load your save, whatever you picked previously will be missing, even after closing the game.
* Apparently, interacting with #4 in the night won't properly advance a day, even if it does advance time to early morning