I installed a fresh new WordPress.
Then uploaded the jevelin.zip without activating it.
Then uploaded the jevelin-child.zip and activated it.
As soon as I activated it the errors started.
Please see the image attached.
Solution for this topic
Sorry to hear of the problem you are having.
Please make sure you are using latest version of PHP on your server by referring the information provided in the following page.
This is a simple PHP warning/notice and most of the time it doesn’t affect functionality of site so it is nothing to worry about!
Do you have WP_DEBUG set to true in your wp-config.php file?
If you do then please set it to false.
This will hide the warning messages and you will be able to use your site normally.