These are warnings not Errors. Please make sure that you are using the latest version of PHP, with the latest version of woocommerce and our theme.
Then check back. If the issue still occurs then provide with the admin panel login details of the website to check it myself and help you out accordingly.
If it happens with the child theme then there is some PHP code there that causes the error. You can fix or remove the code to resolve the problem or switch to the parent theme completely.