<div class="parent">
    <span class="menu">1</span>
    <div class="child">2</div>
    <div class="child">3</div>
    <div class="child">4</div>
</div>

<div class="parent">
    <span class="menu">1</span>
    <span class="menu">2</span>
    <div class="child">3</div>
</div>

.parent {
  width: 200px;  
}

.child,
.menu {
  display: block;
  width: 100%;
  height: 40px;
  margin-bottom: 20px;
}

.child {
  border: 1px solid red;
}

.menu {
  border: 1px solid green;
}

.child:only-of-type,
.menu:only-of-type {
   height: 20px;
}