How can I point out each child line to the parent line account

HI All ,

I know that GL class code for free goods lines come from lines types P40205.

But for parent item it come from item branch plant and it will very time to time.

for free good it is always same as it is coming from line type set up as it P40205.

for eg.

Parent line : 1.0 having GL class code GK101

Child line   :  1.1 free goods GL class Code MN105

Parent line : 2.0 having GL class code AB202

Child line   :  2.1 free goods GL class Code MN105.

Regards,

Anish.