discount condition at header on service contract

Hi Gurus,

In our scenario of service contract. we create  child items with reference to parent item . parent item carries the billing plan. when we apply discount on header of contract, it passing to child items and parent item. which meas on the header , discount getting applied 2 times(one from the child items and one directly ) which we dont want.

how to avoid discount condition type directly on parent item

Thanks,

saaru