function of parent not working in childtheme

For inherited parent theme you need to add Template lines in child theme. Please read this https://codex.wordpress.org/Child_Themes

            /*
             Theme Name:   Twenty Fifteen Child
             Theme URI:    http://example.com/twenty-fifteen-child/
             Description:  Twenty Fifteen Child Theme
             Author:       John Doe
             Author URI:   http://example.com
             Template:     twentyfifteen
             Version:      1.0.0
             License:      GNU General Public License v2 or later
             License URI:  http://www.gnu.org/licenses/gpl-2.0.html
             Tags:         light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
             Text Domain:  twenty-fifteen-child
            */

Here “Template: twentyfifteen” is important to call parent theme. Please check this in your child theme.

Also you can use this plugin to generate child theme. https://wordpress.org/plugins/one-click-child-theme/

I hope this will help you solve your problem.