Update: Oct. 23, 2015
QuickBooks Online is changing the way it handles item hierarchy. This change will affect the way end-users see item hierarchies in QuickBooks Online; it is important that developers understand the changes, especially if their application reads, updates, or creates items in an hierarchy inside the QuickBooks Online APIs.
New Oct. 23, 2015: For a deeper dive, see this post.
Very soon, QuickBooks Online will be migrating from a parent-child system of items to one that is oriented around categories of items. This will better match how the hierarchies are actually being used. Conceptually, the two systems are very similar: instead of many sub-items rolling up into a parent item, those items will be contained inside of a category.
If you use any kind of item hierarchy in your application you will need to update your app to ensure that it works with the new classification.
We have a newly updated page in our documentation that goes over transitioning to category based items, as well as an updated API reference page for item. Note that this is an update with the new minor version 4, so you will have to update your API endpoints in order to use it.
The development sandbox has already been updated with this new change, so please take a look at the new documentation and think about how you will transition your app to the new category structure.
Have questions, comments, or concerns? Please share them on our developer forums.