Avoid keeping track of two lists of nodes during parsing.

lib/liquid/block.rb

@@ -14,9 +14,6 @@ module Liquid
       @nodelist ||= []
       @nodelist.clear
 
-      # All child tags of the current block.
-      @children = []
-
       while token = tokens.shift
         case token
         when IsTag
@@ -31,7 +28,6 @@ module Liquid
               new_tag = tag.parse($1, $2, tokens, @options)
               @blank &&= new_tag.blank?
               @nodelist << new_tag
-              @children << new_tag
             else
               # this tag is not registered with the system
               # pass it to the current block for special handling or error reporting
@@ -43,7 +39,6 @@ module Liquid
         when IsVariable
           new_var = create_variable(token)
           @nodelist << new_var
-          @children << new_var
           @blank = false
         when ''.freeze
           # pass
@@ -64,8 +59,8 @@ module Liquid
       all_warnings = []
       all_warnings.concat(@warnings) if @warnings
 
-      (@children || []).each do |node|
-        all_warnings.concat(node.warnings || [])
+      (nodelist || []).each do |node|
+        all_warnings.concat(node.warnings || []) if node.respond_to?(:warnings)
       end
 
       all_warnings