Simple SDL Tridion / Web GUI extension to set an advanced publish setting by default.

SetPublishToChildrenDefault.config

<?xml version="1.0"?>
<Configuration xmlns="http://www.sdltridion.com/2009/GUI/Configuration/Merge"
               xmlns:cfg="http://www.sdltridion.com/2009/GUI/Configuration"
               xmlns:ext="http://www.sdltridion.com/2009/GUI/extensions"
               xmlns:cmenu="http://www.sdltridion.com/2009/GUI/extensions/ContextMenu">

    <resources cache="true">
        <cfg:filters />
        <cfg:extensiongroups>
            <cfg:extensiongroup name="SetPublishToChildrenDefault">
                <cfg:extension target="Tridion.Web.UI.Controls.RibbonToolbar">
                    <cfg:insertafter>SetPublishToChildrenDefault</cfg:insertafter>
                </cfg:extension>
            </cfg:extensiongroup>
        </cfg:extensiongroups>
        <cfg:groups>
            <cfg:group name="SetPublishToChildrenDefault">
                <cfg:fileset>
                    <cfg:file type="script">SetPublishToChildrenDefault.js</cfg:file>
                </cfg:fileset>
            </cfg:group>
        </cfg:groups>
    </resources>
    <definitionfiles />
    <extensions>
        <ext:editorextensions/>
        <ext:dataextenders/>
    </extensions>
    <commands />
    <contextmenus />
    <localization />
    <settings>
        <defaultpage />
        <navigatorurl />
        <editurls/>
        <listdefinitions/>
        <itemicons/>
        <theme>
            <path/>
            <resourcegroup />
        </theme>
        <resourceextensions>
            <resourceextension>SetPublishToChildrenDefault</resourceextension>
        </resourceextensions>
        <customconfiguration/>
    </settings>
</Configuration>

SetPublishToChildrenDefault.js

$evt.addEventHandler($display, "start", onPublishPopupOpenToSetPublishDefaultToUnCheckAllTargets);

// Event Handler to check off the advanced publish setting.
function onPublishPopupOpenToSetPublishDefaultToUnCheckAllTargets () {
    $evt.removeEventHandler($display, "start", onPublishPopupOpenToSetPublishDefaultToUnCheckAllTargets);

    if ($display.getView().getId() == "PublishPopup") {
		  jQuery("#propagateInChildren").prop("checked", true);		
    }   
}

System.config

<?xml version="1.0" encoding="utf-8"?>
<Configuration xmlns="http://www.sdltridion.com/2009/GUI/Configuration" xmlns:ext="http://www.sdltridion.com/2009/GUI/extensions">
  
  ...
  
  <!-- Editors settings. -->
  <editors default="CME">

    <!-- Customization -->
    <editor name="SetPublishToChildrenDefault">
      <installpath>C:\Program Files (x86)\SDL Web\web\WebUI\Editors\SetPublishToChildrenDefault</installpath>
      <configuration>SetPublishToChildrenDefault.config</configuration>
      <vdir>SetPublishToChildrenDefault</vdir>
    </editor>
    
    ...
  
  </editors> 
  
  ...
  
</Configuration>