OK, gotcha...
What it sounds like is that the child objects you have previously mapped, in the properties you've chosen for mapping, there is dynamic information. The ID's are different or some text string is different or something. This is actually not unusual. Many applications build child components "on the fly" and so there's a lot of variability in the component properties. You have two things you can do:
1) Examine the mapping you have for the child objects and see if you can find some combination of properties that will identify the object that does not change from run to run OR
2) Use some wildcards (*) in your mapping properties to replace some of the strings with the wildcard to allow for the dynamic information.
Without knowing the specifics of your application, the properties being used, etc., I can't be more specific than that.