I've isolated the source of a fatal error that's been occurring when a brand new site is previewed just after installing and activating the plugin I'm working on.

The problem appears to be that the "category_children" item in the options table is not being created.

Interestingly, it appears that two actions trigger WP to create the category_children option. They are: (1) Activating a theme that contains code to create categories and (2) Simply accessing the category manager.

If I do either of those, after activating the plugin, the category_children option is being created (presumably due to checks in the theme activation or the edit-tags.php load) and the error goes away.

Here's the code I'm using in my plugin to create the categories (executes on plugin activation only):


What am I missing? Do I need to explicitly call a method to have WordPress generate the category_children options array for these items?

UPDATE: Thanks to scribu's help below on the reason for this bug, I've found that the PARTIAL fix for this bug is to place this line just after my wp_create_category() calls are complete:


However, this does not work when called in the same plugin that creates the categories. I had to place it in a standalone plugin that's activated separately from the plugin that creates my categories.

2 Answers 2


This is a known (and nasty) bug in the taxonomy hierarchy caching code:


Basically, you have to force a refresh by deleting the option.

  • Hi Scribu, thanks for posting this. +1 for that! I've been pulling my hair out trying to figure it out. I'll check out the bug report and your suggested workaround.
    – Scott B
    Commented Apr 19, 2011 at 17:42
  • @Scribu: if the option does not exist (verified by viewing options.php) does manually deleting it still work as the workaround?
    – Scott B
    Commented Apr 19, 2011 at 17:45
  • Just to be clear, I just need to call delete_option("category_children") after creating my parented categories? Sorry, but I didn't see a reference to the workaround in the bug track comments.
    – Scott B
    Commented Apr 19, 2011 at 18:06
  • Update: fix is to place this line after the category inserts > clean_term_cache('','category');
    – Scott B
    Commented Apr 19, 2011 at 18:39
  • Update 2: There appears to be a problem when calling the clean_term_cache fix above, from the same plugin, at the same time that the categories are created. I can place the call in a stand alone plugin and run it after the first plugin and it works, just not in the same plugin that creates the cats.
    – Scott B
    Commented Apr 19, 2011 at 19:42

Had the same issue. It was solved adding: delete_option("category_children")

After inserting the categories, apparently this flushes the cache for categories. The other workarounds didn't do the trick for me.

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