Here’s some info on the post formats in GP: https://generatepress.com/forums/topic/post-formats/#post-167186
There shouldn’t be any difference between them in the child theme vs GP itself.
The only thing the child themes do is change the design settings, so switching between the parent theme and child theme will change the design.
However, the child themes are built to only change the defaults, so if you’ve gone in and changed some settings and saved them, those saved settings will still be there if you change child themes (no one likes losing their settings).
To start from scratch using one of the child themes, you can reset the settings in “Appearance > GeneratePress”.
Hope this helps 🙂