My 10 year old is a CKIA and is constantly telling me how to take care of his baby brother. It's a good thing I've got him to tell me things, I don't know how he and his older brother got to their preteens without my knowing how to feed a toddler, change a toddler, etc.
When Piratebabe was really little he kept trying to tell me how to properly hold him. Again, how on earth he and his brother managed to get to 12 and 10 respectively without him telling me this is beyond me.
He makes things up too about how things work and insists he's right by saying "Well I've heard that/People tell me things/but it just makes sense!!" Now if he was just telling me something he learned in school and was fascinated by, I'd be interested to hear. But the "I know more than you" attitude he gets is annoying.