Looks like you're Suffering from Buffering.  When I add $|=1; to your script, I get all the output (including from the grandchildren) in out.txt: 

I am running
Process group Id:12773
Process group Id:12773
I am running
Process group Id:12773
Process group Id:12773
I am running
Process group Id:12773
Process group Id:12773
Process group Id in child:12773
I am child and I'am running
I am running
Process group Id in child:12773
I am child and I'am running
Process group Id:12773
Process group Id:12773
Process group Id in child:12773
I am child and I'am running
Process group Id in child:12773
I am child and I'am running
I am running
Process group Id:12773
Process group Id:12773
Process group Id in child:12773
I am child and I'am running
Process group Id in child:12773
I am child and I'am running
I am running
Process group Id:12773
Process group Id:12773
Process group Id in child:12773
I am child and I'am running
Process group Id in child:12773
I am child and I'am running
Process group Id in child:12773
I am child and I'am running
I am running
Process group Id:12773
Process group Id:12773

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In reply to Re: Redirect the process group stdout to parent by almut
in thread Redirect the process group stdout to parent by Anonymous Monk

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