Don't know if it will stay exposed, but I added a search condition for child notes (e.g. find the parent containing a child matching the specified text)

chrome/content/zotero/xpcom/search.js

@@ -663,6 +663,12 @@ Zotero.Search.prototype._buildQuery = function(){
 						openParens++;
 						break;
 					
+					case 'childNote':
+						condSQL += "itemID IN (SELECT sourceItemID FROM "
+							+ "itemNotes WHERE ";
+						openParens++;
+						break;
+					
 					case 'fulltextWord':
 						condSQL += "wordID IN (SELECT wordID FROM fulltextWords "
 							+ "WHERE ";
@@ -1168,6 +1174,16 @@ Zotero.SearchConditions = new function(){
 				field: 'note'
 			},
 			
+			{
+				name: 'childNote',
+				operators: {
+					contains: true,
+					doesNotContain: true
+				},
+				table: 'items',
+				field: 'note'
+			},
+			
 			{
 				name: 'creator',
 				operators: {

chrome/locale/en-US/zotero/zotero.properties

@@ -283,6 +283,7 @@ searchConditions.collectionID	= Collection
 searchConditions.itemTypeID	= Item Type
 searchConditions.tag			= Tag
 searchConditions.note			= Note
+searchConditions.childNote	= Child Note
 searchConditions.creator		= Creator
 searchConditions.thesisType	= Thesis Type
 searchConditions.reportType	= Report Type