What should the name plate actually say?
First name, nickname, or something else entirely.
For a nursery, the first name almost always wins. It is short, it is the word the child will recognise first, and it stays true for the next eighteen years. Formal full names look right on a certificate and cramped on a door.
Nicknames are the other good answer, and often the warmer one. If everyone in the house calls her Pihu, the plate that says Pihu is the one that belongs to the room. You can always order the formal version later for a study desk.
Dates work too. A short date of birth — 14.02.2019 — fits inside the twelve-character limit and turns the plate into a keepsake rather than a label, which is a common choice for a naming-ceremony gift.
Siblings sharing a room usually want two plates rather than one. Two names on a single line means two sets of narrow letters; two plates side by side means each child has their own, which is the point of the thing.