Ask your child to draw the room as a bird would see it looking straight down — not as they see it from where they stand.
Start together with the four walls, then let them place the furniture. Expect a mix of overhead and side-on views; that is normal.
When it is done, use it: put a small object somewhere and mark the spot on the map, then have someone find it using only the drawing.
An overhead view has to be constructed mentally because it is never actually seen, which makes it a genuine act of spatial transformation. Using the finished map to find something tests whether it represents reality rather than merely resembling it.