I have seen in the feedback-bug page: http://feedback.wikidot.com/bug:855 breadcrumbs Error on custom layout that
the used **[[breadcrumb]] does nit work.

I have inserted the parent page (home) on Overview and About.

There is also the breadcrumb module missing…

The module is [[breadcrumbs]], not [[breadcrumb]]. As it's stated at Documentation.

I just inserted breadcrumbs into the layout just above the content section using this code:

    <hr>
    [[if breadcrumbs]]
      <div class="breadcrumbs">
        [[breadcrumbs]]
      </div>
    [[/if]]
    [[content]]

I also added some CSS styling for the .breadcrumbs class.

/* Breadcrumbs styling */
.breadcrumbs {
    margin: -15px 0 10px 0;
    font:italic bold 12px/20px Arial, sans-serif;
}