Meteor Helper inheritance

<template name="parent">
    {{>Template.contentBlock}}
</template>

<template name="child1">
    {{#parent}}
    <div class="whateverDiv"> 
        <a href="#">{{parentHelper}}</a> 
    </div>
    {{/parent}}
</template>
<template name="child2">
   {{#parent}}
    <span class="whatever"> {{parentHelper}} </span>
   {{/parent}}
</template>

The problem you have with this is that you can't access to parent helpers from the block template.
What I did is this:

var helpers = {
    parentHelper: function () {
      var data = fetchDataFromSomeWhere();
      return data;
    }
};

Template.parent.onCreated(function () {
    Template.parent.__liveInstances = Template.parent.__liveInstances || 0;
    Template.parent.__liveInstances++;
    //Here you can do whatever is common for all the child templates, subscribing to a publication, etc.

    //Register global helpers as local helpers
    if (Template.parent.__liveInstances > 0) {
        _.each(_.keys(helpers), function (helperName) {
            Template.registerHelper(helperName, helpers[helperName]);
        });
    }

});


Template.parent.onDestroyed(function () {
    //"Unregister" helpers
    Template.projectListInfo.__liveInstances--;
    if (Template.projectListInfo.__liveInstances === 0) {
        _.each(_.keys(helpers), function (helperName) {
            Template.registerHelper(helperName, _.noop);
        });
    }

});