WordPress Multisite allows site owners to create multiple blogs within a single installation; think WordPress.com. With all of the features and functionality offered there is one thing missing – the ability to select the theme used when a new sub-site is created.
Fortunately, the solution is pretty simple. All you need to do is add a line or two of code to your wp-config.php file.
To insert the code locate the area in your wp-config with your multi site settings (define(‘MULTISITE’, true);).
Then paste the code below that line</em> and above
<em>/* That’s all, stop editing! Happy blogging. */.</em>