code: public void setChildrenFollowInput(final boolean follow) {
          if (follow != mChildrenFollowInput) {
              mChildrenFollowInput = follow;
              for (Widget child : getChildren()) {
                  child.registerPickable();
              }
          }
      }
docs: When children follow the input of their parent {@link Widget}, the parent
  and children are treated as a single entity for touch event purposes.
  When any of them would normally get a touch event, they all get a touch
  event.
  <p>
  The touch hook method -- {@link Widget#onTouch()}  -- is invoked as
  usual, but en masse for the parent and its children. There is one caveat:
  only the parent's {@code onTouch()} method determines whether the touch
  event is accepted or rejected. If the parent rejects the event, it is
  rejected for the entire group and none of the children will have
  {@code onTouch()} called on them.
  <p>
  Children can {@linkplain #setTouchable(boolean) enable and disable} touch
  individually; if a child disables touch, it will not receive calls to
  {@code onTouch()}, but it will still be considered for dispatching touch
  events to the entire group. However, if the parent disables touch,
  neither it nor any of its children will receive touch events.
  
  @param follow
  {@code true} to enable children following input, {@code false}
  to disable.