Child theme

I created a child theme to make changes to the site. I am trying to change widget h1 tags, and post navigation h1 tags, and others. I uploaded the widgets.php file and the templates-tag.php file to the child theme. I changed the title tags but the it did not work. If I make the changes at the core, it works. I changed the title tags in the content.php file and it worked. So I am confused about why some changes are working, and others are not. Please help.