Best way to add multiple child records at once?

1. How do I add multiple records to a flow in Salesforce?
2. Can we update all child records in process builder?

How do I add multiple records to a flow in Salesforce?

To create multiple records, you must use the values from a record collection variable. Earlier in the flow, populate the record collection variable with the new records' field values. When you use a record collection variable to create multiple records at once, you reduce the number of DML requests in your flow.

Can we update all child records in process builder?

Process Builder: You can use process builder to update parent record from child.