Design issues

I am creating a windows application in C # and I have the following design question:

I have the following object structure: Parent -> Kids Collection -> Child -> Grandchildren Collection -> Grandchild.

The use case requires me to use my parent in stages. For example. Create a new instance of the parent. Fill in the parent and save. At a later stage, I would take the parent and fill in the children and save. In the final step, I would pick the parent again and populate the grandchildren for specific child objects and save.

Is this a bad object model? If so, how can you break down this huge object model into smaller models?

thank