Thanks for reporting.
That warning message says the warning occured in category-131.php of the thema you are using.
I guess you need to edit category-131.php( as parent template ) to handle child category’s entries.
The WordPress category template handles only one category id or slug normally. This case it is category id = 131.
If category 131 has any children for example id = 132 and 133, category-131.php need to handle entries of category 131, 132, 133.
I should have explained in the reademe.txt this.
I can improve the document by your repot. Thanks you.
Please tell me if my English is confusing.
