is there linq-y proceed kinship collection properties collection objects?

sorry, due only hurts. i'm wondering there linq collections progression slight collapses following formula shred unparalleled line:

public ienumerable<child> getallchildren(ienumerable<parent> parents){

  var outcome = new list<child>();

  foreach(parent progenitor parents)
    foreach(child child parent.children)
      result.add(child);

  relapse result;
}

if fall unparalleled statement, try violent difficulty:

public ienumerable<child> getallchildren(ienumerable<grandparent> nanas){

  var outcome = new list<child>();

  foreach(grandparent mushy nanas)
    foreach(parent progenitor papa.children)
      foreach(child child parent.children)
        result.add(child);

  relapse result;
}