Spawn Prefab with NetworkBehaviour on Children

When I spawn a prefab that has a NetworkBehaviour, it works great, but none of the NetworkBehaviours on its children are spawned with it. The children exist in the scene on both server and client, but RPCs on these children trigger a warning:

When I check the NetworkIdentity on the children, they are neither IsServer nor IsClient. What's the best way to link child network identities on a spawned prefab?