diff --git a/family-tree.cabal b/family-tree.cabal
--- a/family-tree.cabal
+++ b/family-tree.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.3.1.2
+version:             0.3.1.3
 
 package-url:         https://github.com/Taneb/family-tree
 
diff --git a/src/Data/FamilyTree.hs b/src/Data/FamilyTree.hs
--- a/src/Data/FamilyTree.hs
+++ b/src/Data/FamilyTree.hs
@@ -452,9 +452,9 @@
     \fam -> fam &
             head1 %~ (id & ix (Just $ PersonID n) .~ Nothing) &
             head2 %~ (id & ix (Just $ PersonID n) .~ Nothing) &
-            children . ix n .~ False
+            children . contains n .~ False
             ) &
-  events %~ IM.map (eventAttendees . ix n .~ False)
+  events %~ IM.map (eventAttendees . contains n .~ False)
 
 -- | Deletes a family from the family tree, removing all references to it.    
 deleteFamily :: FamilyID -> FamilyTree -> FamilyTree