Question: Link was an infant when he was delivered to and raised by the Kokiri, who don't age. When Link becomes a child, they should've realised that he wasn't a Kokiri because he aged. Why didn't they see this?
Question: Does the Mask of Truth do anything for the player besides allow them to see secret messages in the stone clocks?
Chosen answer: There is another thing it does for the player. Deep in the Lost Woods is an area with two creatures that will sell the player items. Look for where you see a bunch of butterflies gathered. Head toward them and you will fall into a hole. When you land put on the Mask of Truth and slowly walk forward. Some Deku creatures will pop out and look at you. After this talk to the big Deku creature to the right and he will increase your ability to hold more Deku nuts. Wearing other masks from the Happy Mask shop will also have different reactions from the Deku Scrubs.
Answer: Because the Kokiri don't age past a certain age, but they do age up to that age. Link looked roughly the same age as the other Kokiri when his adventure started, which is why they never noticed that he was different.