Definitely an issue in this house too. Our boys are 19 months apart and while the older DS5.5 is now learning to read cat / hat / fat, the younger one has been reading words like that since just after turning 2 and is now at close to 4 years old interested in reading childrens books titled "Quotations from Shakespeare" and alike. The younger one picks up everything instantly but because of being very 2E you don't know what he knows unless you spend every day with him. The older one is only slightly 2E. The older one rocks when it comes to math but the younger one could learn what the older one knows in a matter of couple days if he had interest in it. They are still too young to realize they learn with different speeds but I'm sure eventually it will come up.
