A child theme is a theme that inherits its functionality from another theme, the parent theme. Child themes are often used when you want to customize or tweak an existing theme without losing the ability to update the parent theme.
After the Bosa Pro Theme Purchased from Pricing page, you can download the zip file of the Bosa Pro (Parent) Theme. Every child theme needs to have the parent theme in the same root to work.
Click below button to Download Free Starter Child theme for Bosa Pro: