Child accounts are created by the Account Owner of a Parent account - the Account Owner has permission to share items with them which can be used in the Child account.
Example
Ben is the Account Owner of a Parent account. He has one Child account that Lisa sits in. He has created a Newsletter template that he wants Lisa to use each month to keep their team up to date. He has shared the template to her account, making it available for her to use.
What can be shared to a Child Account?
Menus
Tags
Styles
Analytics
Security rules
Badges
Notifications
Templates
TigerKits
How to share items to a Child Account
Select 'My Account' > 'Users'.
Select the 'Child Accounts' tab to view the Child Accounts and users beneath your Parent Account.
Select the item type you want to share, for example 'Templates'.
Select the Permission checkbox to share.
Select 'Save'.