https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/t4114/canada-child-benefit.html#share_custody
"Do you share custody of a child?
You share custody of a child if the child lives with two different individuals in separate residences on a more or less equal basis, such as:
the child lives with one parent four days a week and the other parent three days a week
the child lives with one parent one week and the other parent the following week
any other regular cycle of alternation
In these cases, both individuals may be considered primarily responsible for the child’s care and upbringing when the child lives with them. Each individual will get 50% of the payment they would have received if the child lived with them all of the time.
If you have just entered into a shared custody situation for your child(ren), you have to apply for the benefits (see How do you apply?). If you already get the benefits, you have to tell us by using one of the following methods:
"Apply for child benefits" in My Account
calling 1-800-387-1193
sending Form RC66, Canada Child Benefits Application, indicating shared custody
sending a letter explaining the shared custody situation
Your payments will be recalculated accordingly.
For more information, go to Canada child benefit or call 1-800-387-1193. "