Function sp_io::storage::child_get

pub fn child_get(
    child_storage_key: &[u8], 
    child_definition: &[u8], 
    child_type: u32, 
    key: &[u8]
) -> Option<Vec<u8>>

All Child api uses :

• A child_storage_key to define the anchor point for the child proof (commonly the location where the child root is stored in its parent trie).
• A child_storage_types to identify the kind of the child type and how its child definition parameter is encoded.
• A child_definition_parameter which is the additional information required to use the child trie. For instance defaults child tries requires this to contain a collision free unique id.

This function specifically returns the data for key in the child storage or None if the key can not be found.