As far as I know, you have two options.

Option 1)

Null all the child objects, this will ensure EF not to add anything. It will also not delete anything from your database.

Option 2)

Set the child objects as detached from the context using the following code

context.Entry(yourObject).State = EntityState.Detached

Note that you can not detach a List/Collection. You will have to loop over your list and detach each item in your list like so

foreach (var item in properties)
     db.Entry(item).State = EntityState.Detached;