Unlocker

Maddie, standing about halfway up the stairs looking down at the first
floor bathroom door: "Daddy, how are you gonna get the unlocker?

Daddy: "The what!?!"

Maddie: "The unlocker (starts pointing above the bathroom door)"

Daddy: "Oh, you mean the key!!!" (there's a key on the ledge above each
bathroom door in case someone locks themselves in!)

How cute, unlocker! That's what a key does!