insert "Posted on:" in front of blog post dates

How?

I would like this edit to be global everywhere the blog posts show, so both on blog overview and single post view and also if I on some page have added the blog element in enfold page editor.

Perhaps on a child theme so edits wont be lost or if you know a plugin (I have searched and searched but can´t find any that I can use)

thanks in advance! :)