Is it true that Link has the Triforce of Courage symbol on his hand in the child ending? What does this imply?
Well it is clear that this is not a simple rumour, but a fact, as shown in this picture: The implication of this is clear, that the splitting of the Triforce has already happened in the Child Timeline. The alternative would be that Link has brought his Triforce shard from the Adult Timeline, but that would mean that there are two Triforces of Courage in the Child Timeline (Links and the one in the Sacred Realm), and none in the Adult one.