>I use a parameterized view to display child records in a grid. When I edit one of them I get this message before it saves. Then it saves the same change to the field in all records for that parent. Since the table on which the view is based is strictly a child, I didn't make a keyfield. Do I have to create a keyfield for the child table and include it in the view (defining it as a keyfield in the view) or can I change something else in the view designer to make it update to the child table without errors?

You must have unique key field(s). You can set them in View designer.