So you have Buddypress installed, theme activated and everything is working but, Buddypress is not working on your child themes. Are they buddypress compatible? – If they are and you have no other solutions. Make sure to BP enable Multiblog by adding the following to your Wp-config.php file.

define ( ‘BP_ENABLE_MULTIBLOG’, true );

Want to change the Root Buddypress location

Replace $blog_id with the ID of the blog you want to set up as the Root.

config.php:
define ( ‘BP_ROOT_BLOG’, $blog_id );
Example:
define ( ‘BP_ROOT_BLOG’, 2 );

Simple, little things you can do to move forward.