Federated Multiple Office 365 domain into Active Directory Federation Services 2.0 Farm

I want to federated multiple office 365 domain (example: @abc.com, @child.abc.com) into single ADFS farm. The scenario as below:

I have single Active Directory Forest, with one parent domain (example: abc.com) and one child domain (example: child.abc.com).

Currently my parent domain(abc.com) had federated with office 365 domain(@abc.com) using ADFS farm and my child domain(child.abc.com) had federated with office 365 domain(@child.abc.com) using single ADFS server. 

How to federate my child domain(child.abc.com) into ADFS farm?