get_term_children() has incorrect @return value

[SergeyBiryukov]

See tags/3.8.1/src/wp-includes/taxonomy.php#L1071​.

It returns an array of term IDs, not term objects.

[wonderboymusic]

It's primary (and really only use) is in WP_Tax_Query::clean_query() to populate the terms property with term_id array

[wonderboymusic]

In 27457:

get_term_children() returns an array of IDs, not objects. The docs have been updated to reflect this.

Fixes #27312.