Programatic Switching with Child Themes

switching themes on the fly using the following approach

add_filter(‘template’, $templatename);
add_filter(‘stylesheet’, $templatename);

as a plugin (when done within functions.php, oh boy, the header.php wasn’t switching and it was a mess.. any thoughts on this also appreciated).

When done with “full bodied” themes, works great. When I try to switch to a child theme, it blows up (blank browser page). The child theme works just fine when activated from the dashboard directly. The child theme, at this stage, is only a style.css that imports the parent’s css.

Any thoughts on where this is going wrong or on a work around? TIA!