The surefire way to identify an eager beaver young reader is to listen to them.
How do they pronounce the words they’ve seen in print but never heard?
Do they — as I remember being sniggered at for doing — say “causal” instead of casual? Does that understandably precocious child pronounce “foregin” in place of that odd-looking word foreign? And — as I heard an adult enunciate when expanding his horizons into less mundane topics — does “esoteric”sometimes emerge (by analogy with “expectorate” perhaps — with the stress on the second syllable?