Need separate and independent execution of (child) package

I'm looking around for an SSIS solution that would basically start one non-blocking process, and continue on immediately with another.   This is similar to EXEC msdb.dbo.sp_start_job @job_name = 'Job to Branch' except that I'd like to have the parent process succeed immediately.

This apparently doesn't work with the ExecuteOutOfProcess property = True in the parent job.  I first tried running a job step, i.e. Job Step 2, but if Job Step 1 was already running, I couldn't trigger Job step 2 with T-SQL.

Could anyone suggest a way to start a child package and continue on with the main branch in the parent -- I'm guessing the terminology would be 'asynchronous execution' but I'm not really sure.

Thanks,
Clovis