This was a pretty neat demo! I thought the timer and showing only the silhouettes of the items you're collecting were a good way to add some challenge. Especially on the playground level, there are a few places where the objects you're looking for will blend right in to the environment, so encouraging people to search by shape rather than color worked well - plus, a nice bonus is that it adds some accessibility for folks with color blindness.
I think something that could take the final version to the next level is more interactivity. The closet door in the beginning is a great example, and a lot more of that would be fun. Moving things around, opening/closing curtains, drawers, etc. Just something I noticed though is that you can sometimes click through interactive objects (i.e. you can click on the wallet in the 1st level and collect it without opening the closet door).
It could be cool to see more with Karla, too - if it wasn't for the title and seeing her on the main menu, I'd have just assumed the game is in first-person and we're playing as ourselves.
All in all, this was a good start, hope to see it expanded upon!