How to Move On Child Gridview From Parent Gridview On Down Key

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C#2.0

C#

Hello,
I am using Data grid view(Master) for storing value of a product.When i type in cell, according to alphabets typed products are listed in the another data grid view(Child) which is displaying just bellow the row where i typed the product name.I am trying to do if the child grid view is visible then on down key press the focus should move to the child grid view.
How To Do this???? Pls Help.