Making relations before save

Question

Hi. I´m using subsonic 3. I´m need pass a parent object with his childs to a custom method before they are persisted , like this:

Public Function ValidateParent(parent as Parent) as Boolean  
    For Each child in parent.Childs  
         ValidateChild(child)  
    Next  
    Return true  
End Function

I'm trying to set the Parent.childs collection, but it's readonly. Some idea?