Now that I’ve had two toddlers, I can firmly state that this eighteen-month to two-year phase is definitely the era of the random object found in the random place.
I’m not sure why toddlers like to stash things around, but it must have some evolutionary survival roots.
My older child used to take the letter magnets from the fridge and shove them between the mattress and the box spring in our bedroom.
The second child seems to have a wider spectrum of both objects and locations.
Look what I found around my house:
What has your toddler left around the house?