Originally Posted by
montwila
Koi are generally not cannibalistic.
Not knowing your pond. Is there a place they could be hiding such as inside a plants vegetation or under a rock? If they are starving then maybe a 2" koi is the same as a dragonfly larvae to a 17" fish as Orlando suggests.
If your goldfish pond has temperature swings and the koi pond does not. Then sequester the babies in a place the older/larger koi cannot get to in your koi pond. I often use floating cages when adding fingerlings to my lower pond. It keeps them up where I can see them and away from the larger fish. They get first chance at their food and the bigger fish do not bother them. Likewise they stay out of the way of the bigger fish's mouths. As Rich or Graham would say: Anything that goes in a koi's mouth is food until proven otherwise.