diff --git a/src/FssTreeItem.ts b/src/FssTreeItem.ts
index 7a54bfc..18a0d0b 100644
--- a/src/FssTreeItem.ts
+++ b/src/FssTreeItem.ts
@@ -12,6 +12,7 @@ import { INotebookTracker } from '@jupyterlab/notebook';
 import { fileIcon, folderIcon } from '@jupyterlab/ui-components';
 
 import { FssTreeItemContext } from './FssTreeItemContext';
+import { formatBytes } from './utils';
 import { Logger } from './logger';
 
 export class FssTreeItem {
@@ -159,17 +160,38 @@ export class FssTreeItem {
     });
   }
 
-  setMetadata(user_path: string, size: string) {
+  setMetadata(user_path: string, size: string, childrenCount?: number) {
     this.logger.debug('Setting item metadata', {
       path: user_path,
-      size
+      size,
+      childrenCount
     });
 
     this.root.dataset.fss = user_path;
     this.root.dataset.fsize = size;
 
-    const sizeDisplay = `(${size.toLocaleString()})`;
-    this.sizeLbl.innerText = sizeDisplay;
+    if (childrenCount !== undefined) {
+      // For directories, show children count
+      const childrenDisplay = `(${childrenCount} item${childrenCount === 1 ? '' : 's'})`;
+      this.sizeLbl.innerText = childrenDisplay;
+      this.sizeLbl.style.display = 'block';
+    } else if (this.isDir) {
+      // For directories without known count, hide the size label
+      this.sizeLbl.style.display = 'none';
+      return;
+    } else {
+      // For files, show size
+      const sizeNumber = Number(size);
+      if (isNaN(sizeNumber)) {
+        this.logger.error('Invalid size', { size });
+        return;
+      }
+      const formattedSize = formatBytes(sizeNumber);
+      const formattedSizeString = formattedSize.toString();
+
+      const sizeDisplay = `(${formattedSizeString})`;
+      this.sizeLbl.innerText = sizeDisplay;
+    }
   }
 
   setText(value: string) {
@@ -191,6 +213,7 @@ export class FssTreeItem {
     if (symbol === 'file') {
       fileIcon.element({ container: this.dirSymbol });
       this.isDir = false;
+      this.sizeLbl.style.display = 'block';
     }
   }
 
diff --git a/src/index.ts b/src/index.ts
index 1cce824..1d49894 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -903,13 +903,21 @@ class FsspecWidget extends Widget {
     // Update the TreeView in the UI
     await this.updateFileBrowserView(nodeForPath);
 
+    // Update the children count for the expanded directory
     if (nodeForPath.id.toString() in this.elementHeap) {
       const uiElement = this.elementHeap[nodeForPath.id.toString()];
+      const actualChildrenCount = Object.keys(nodeForPath.children).length;
+      uiElement.setMetadata(
+        nodeForPath.path,
+        nodeForPath.metadata.size,
+        actualChildrenCount
+      );
       uiElement.expandItem();
 
       this.logger.debug('Auto-expanded directory node', {
         path: source_path,
-        nodeId: nodeForPath.id
+        nodeId: nodeForPath.id,
+        childrenCount: actualChildrenCount
       });
     }
   }
@@ -991,10 +999,28 @@ class FsspecWidget extends Widget {
             true,
             this.notebookTracker
           );
-          item.setMetadata(
-            (pathInfo as any).path,
-            (pathInfo as any).metadata.size
-          );
+          const isDirectory =
+            Object.keys((pathInfo as any).children).length > 0 ||
+            ('type' in (pathInfo as any).metadata &&
+              (pathInfo as any).metadata.type === 'directory');
+
+          if (isDirectory) {
+            // Since directroy children are lazy-loaded: set children count to undefined
+            // The count will be updated once the directory is expanded
+            item.setMetadata(
+              (pathInfo as any).path,
+              (pathInfo as any).metadata.size,
+              undefined
+            );
+            item.setType('dir');
+          } else {
+            item.setMetadata(
+              (pathInfo as any).path,
+              (pathInfo as any).metadata.size
+            );
+            item.setType('file');
+          }
+
           item.setText(pathSegment);
           item.treeItemClicked.connect(this.handleTreeItemClicked.bind(this));
           item.getBytesRequested.connect(
@@ -1008,18 +1034,6 @@ class FsspecWidget extends Widget {
           (pathInfo as any).id = item_id;
           this.elementHeap[item_id.toString()] = item;
 
-          // Set the item type (file or directory)
-          const isDirectory =
-            Object.keys((pathInfo as any).children).length > 0 ||
-            ('type' in (pathInfo as any).metadata &&
-              (pathInfo as any).metadata.type === 'directory');
-
-          if (isDirectory) {
-            item.setType('dir');
-          } else {
-            item.setType('file');
-          }
-
           // Add children to build targets if needed
           if (Object.keys((pathInfo as any).children).length > 0) {
             buildTargets[(pathInfo as any).path] = [
diff --git a/src/utils.ts b/src/utils.ts
new file mode 100644
index 0000000..884d49c
--- /dev/null
+++ b/src/utils.ts
@@ -0,0 +1,28 @@
+export function formatBytes(n: number): string {
+  /**
+   * Examples:
+   * formatBytes(1)      // '1 B'
+   * formatBytes(1234)   // '1.21 kiB'
+   * formatBytes(12345678) // '11.77 MiB'
+   * formatBytes(1234567890) // '1.15 GiB'
+   * formatBytes(1234567890000) // '1.12 TiB'
+   * formatBytes(1234567890000000) // '1.10 PiB'
+   *
+   * For all values < 2^60, the output is always <= 10 characters.
+   * Note:Code adapted from dask.utils.format_bytes
+   */
+  const units: [string, number][] = [
+    ['Pi', Math.pow(2, 50)],
+    ['Ti', Math.pow(2, 40)],
+    ['Gi', Math.pow(2, 30)],
+    ['Mi', Math.pow(2, 20)],
+    ['ki', Math.pow(2, 10)]
+  ];
+
+  for (const [prefix, k] of units) {
+    if (n >= k * 0.9) {
+      return `${(n / k).toFixed(2)} ${prefix}B`;
+    }
+  }
+  return `${n} B`;
+}