Great read. It's always good to expose juniors to the basics and then gradually move them up to the real work. As you mentioned about using Git , there is a one good project that i found recently in github called First Contributions where newbies can get a exposure of how Git and Github works.They can practice there and once they confident enough then moving them in to the real working branch. Same way there should be a practice project (Playgrounds ) :-) which have some resemblance of the actual project where newcomers can get some hands on practice.
RE: Why Talented Juniors are so important for your software team