Model Binding child gridview within a parent gridview

Hi,
I have a parent gridview, which contains a child gridview. The parent gridview is defined with an ItemType and SelectMethod. The selectMethod returns an IQueryable object which contains the collection for the parent and child gridviews. Only the parent gridview populated with data. In the past, I databinded the child gridview with the parent RowDataBinded event method. My question, I thought the both parent and child would be model binding with collection. Any help is appreciated.