diff --git a/system/src/Grav/Common/Page/Interfaces/PageLegacyInterface.php b/system/src/Grav/Common/Page/Interfaces/PageLegacyInterface.php
index 35d6d2180..1f84b951b 100644
--- a/system/src/Grav/Common/Page/Interfaces/PageLegacyInterface.php
+++ b/system/src/Grav/Common/Page/Interfaces/PageLegacyInterface.php
@@ -367,7 +367,7 @@ interface PageLegacyInterface
     /**
      * Returns children of this page.
      *
-     * @return \Grav\Common\Page\Collection
+     * @return Collection
      */
     public function children();
 
diff --git a/system/src/Grav/Common/Page/Page.php b/system/src/Grav/Common/Page/Page.php
index f467d2cc5..773f1a904 100644
--- a/system/src/Grav/Common/Page/Page.php
+++ b/system/src/Grav/Common/Page/Page.php
@@ -69,7 +69,7 @@ class Page implements PageInterface
     protected $slug;
     /** @var string */
     protected $route;
-    /** @var string */
+    /** @var string|null */
     protected $raw_route;
     /** @var string */
     protected $url;
@@ -89,15 +89,15 @@ class Page implements PageInterface
     protected $frontmatter;
     /** @var string */
     protected $language;
-    /** @var string */
+    /** @var string|null */
     protected $content;
     /** @var array */
     protected $content_meta;
-    /** @var string */
-    protected $summry;
+    /** @var string|null */
+    protected $summary;
     /** @var string */
     protected $raw_content;
-    /** @var array */
+    /** @var array|null */
     protected $metadata;
     /** @var string */
     protected $title;
@@ -115,13 +115,13 @@ class Page implements PageInterface
     protected $order_by;
     /** @var string */
     protected $order_dir;
-    /** @var array */
+    /** @var array|string|null */
     protected $order_manual;
     /** @var bool */
     protected $modular_twig;
     /** @var array */
     protected $process;
-    /** @var int */
+    /** @var int|null */
     protected $summary_size;
     /** @var bool */
     protected $markdown_extra;
diff --git a/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php b/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php
index c49141ead..bb261f8d9 100644
--- a/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php
+++ b/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php
@@ -21,6 +21,7 @@ use Grav\Framework\Cache\CacheInterface;
 use Grav\Framework\File\Formatter\MarkdownFormatter;
 use Grav\Framework\File\Formatter\YamlFormatter;
 use Grav\Framework\Flex\FlexDirectory;
+use Grav\Framework\Flex\Interfaces\FlexCollectionInterface;
 use Grav\Framework\Flex\Interfaces\FlexIndexInterface;
 use Grav\Framework\Flex\Interfaces\FlexObjectInterface;
 use Grav\Framework\Flex\Pages\FlexPageIndex;
@@ -867,8 +868,12 @@ trait PageLegacyTrait
     public function isFirst(): bool
     {
         $parent = $this->parent();
+        $children = $parent ? $parent->children() : null;
+        if ($children instanceof FlexCollectionInterface) {
+            $children = $children->withKeyField();
+        }
 
-        return $parent ? $parent->children()->withKeyField()->isFirst($this->getKey()) : true;
+        return $children instanceof PageCollectionInterface ? $children->isFirst($this->getKey()) : true;
     }
 
     /**
@@ -879,8 +884,12 @@ trait PageLegacyTrait
     public function isLast(): bool
     {
         $parent = $this->parent();
+        $children = $parent ? $parent->children() : null;
+        if ($children instanceof FlexCollectionInterface) {
+            $children = $children->withKeyField();
+        }
 
-        return $parent ? $parent->children()->withKeyField()->isLast($this->getKey()) : true;
+        return $children instanceof PageCollectionInterface ? $children->isLast($this->getKey()) : true;
     }
 
     /**
@@ -913,8 +922,12 @@ trait PageLegacyTrait
     public function adjacentSibling($direction = 1)
     {
         $parent = $this->parent();
+        $children = $parent ? $parent->children() : null;
+        if ($children instanceof FlexCollectionInterface) {
+            $children = $children->withKeyField();
+        }
 
-        return $parent ? $parent->children()->withKeyField()->adjacentSibling($this->getKey(), $direction) : false;
+        return $children instanceof PageCollectionInterface ? $children->adjacentSibling($this->getKey(), $direction) : false;
     }
 
     /**