Update gamepad_viewer to use children macro (#18282)

# Objective

Contributes to #18238 
Updates the `gamepad_viewer`, example to use the `children!` macro.  

## Solution

Updates examples to use the Improved Spawning API merged in
https://github.com/bevyengine/bevy/pull/17521

## Testing

- Did you test these changes? If so, how?
- Opened the examples before and after and verified the same behavior
was observed. I did this on Ubuntu 24.04.2 LTS using `--features
wayland`.
- Are there any parts that need more testing?
- Other OS's and features can't hurt, but this is such a small change it
shouldn't be a problem.
- How can other people (reviewers) test your changes? Is there anything
specific they need to know?
  - Run the examples yourself with and without these changes.
- If relevant, what platforms did you test these changes on, and are
there any important ones you can't test?
  - see above

---

## Showcase

n/a

## Migration Guide

n/a

examples/tools/gamepad_viewer.rs

@@ -132,41 +132,40 @@ fn setup(mut commands: Commands, meshes: Res<ButtonMeshes>, materials: Res<Butto
 
     // Buttons
 
-    commands
+    commands.spawn((
-        .spawn((
         Transform::from_xyz(BUTTONS_X, BUTTONS_Y, 0.),
         Visibility::default(),
-        ))
+        children![
-        .with_children(|parent| {
+            GamepadButtonBundle::new(
-            parent.spawn(GamepadButtonBundle::new(
                 GamepadButton::North,
                 meshes.circle.clone(),
                 materials.normal.clone(),
                 0.,
                 BUTTON_CLUSTER_RADIUS,
-            ));
+            ),
-            parent.spawn(GamepadButtonBundle::new(
+            GamepadButtonBundle::new(
                 GamepadButton::South,
                 meshes.circle.clone(),
                 materials.normal.clone(),
                 0.,
                 -BUTTON_CLUSTER_RADIUS,
-            ));
+            ),
-            parent.spawn(GamepadButtonBundle::new(
+            GamepadButtonBundle::new(
                 GamepadButton::West,
                 meshes.circle.clone(),
                 materials.normal.clone(),
                 -BUTTON_CLUSTER_RADIUS,
                 0.,
-            ));
+            ),
-            parent.spawn(GamepadButtonBundle::new(
+            GamepadButtonBundle::new(
                 GamepadButton::East,
                 meshes.circle.clone(),
                 materials.normal.clone(),
                 BUTTON_CLUSTER_RADIUS,
                 0.,
+            ),
+        ],
     ));
-        });
 
     // Start and Pause
 
@@ -188,20 +187,17 @@ fn setup(mut commands: Commands, meshes: Res<ButtonMeshes>, materials: Res<Butto
 
     // D-Pad
 
-    commands
+    commands.spawn((
-        .spawn((
         Transform::from_xyz(-BUTTONS_X, BUTTONS_Y, 0.),
         Visibility::default(),
-        ))
+        children![
-        .with_children(|parent| {
+            GamepadButtonBundle::new(
-            parent.spawn(GamepadButtonBundle::new(
                 GamepadButton::DPadUp,
                 meshes.triangle.clone(),
                 materials.normal.clone(),
                 0.,
                 BUTTON_CLUSTER_RADIUS,
-            ));
+            ),
-            parent.spawn(
             GamepadButtonBundle::new(
                 GamepadButton::DPadDown,
                 meshes.triangle.clone(),
@@ -210,8 +206,6 @@ fn setup(mut commands: Commands, meshes: Res<ButtonMeshes>, materials: Res<Butto
                 -BUTTON_CLUSTER_RADIUS,
             )
             .with_rotation(PI),
-            );
-            parent.spawn(
             GamepadButtonBundle::new(
                 GamepadButton::DPadLeft,
                 meshes.triangle.clone(),
@@ -220,8 +214,6 @@ fn setup(mut commands: Commands, meshes: Res<ButtonMeshes>, materials: Res<Butto
                 0.,
             )
             .with_rotation(PI / 2.),
-            );
-            parent.spawn(
             GamepadButtonBundle::new(
                 GamepadButton::DPadRight,
                 meshes.triangle.clone(),
@@ -230,8 +222,8 @@ fn setup(mut commands: Commands, meshes: Res<ButtonMeshes>, materials: Res<Butto
                 0.,
             )
             .with_rotation(-PI / 2.),
-            );
+        ],
-        });
+    ));
 
     // Triggers
 
@@ -275,43 +267,35 @@ fn setup_sticks(
     let live_mid = (live_lower + live_upper) / 2.0;
 
     let mut spawn_stick = |x_pos, y_pos, x_axis, y_axis, button| {
-        commands
-            .spawn((Transform::from_xyz(x_pos, y_pos, 0.), Visibility::default()))
-            .with_children(|parent| {
-                // full extent
-                parent.spawn(Sprite::from_color(
-                    DEAD_COLOR,
-                    Vec2::splat(STICK_BOUNDS_SIZE * 2.),
-                ));
-                // live zone
-                parent.spawn((
-                    Sprite::from_color(LIVE_COLOR, Vec2::splat(live_size)),
-                    Transform::from_xyz(live_mid, live_mid, 2.),
-                ));
-                // dead zone
-                parent.spawn((
-                    Sprite::from_color(DEAD_COLOR, Vec2::splat(dead_size)),
-                    Transform::from_xyz(dead_mid, dead_mid, 3.),
-                ));
-                // text
         let style = TextFont {
             font_size: 13.,
             ..default()
         };
-                parent
+        commands.spawn((
-                    .spawn((
+            Transform::from_xyz(x_pos, y_pos, 0.),
+            Visibility::default(),
+            children![
+                Sprite::from_color(DEAD_COLOR, Vec2::splat(STICK_BOUNDS_SIZE * 2.),),
+                (
+                    Sprite::from_color(LIVE_COLOR, Vec2::splat(live_size)),
+                    Transform::from_xyz(live_mid, live_mid, 2.),
+                ),
+                (
+                    Sprite::from_color(DEAD_COLOR, Vec2::splat(dead_size)),
+                    Transform::from_xyz(dead_mid, dead_mid, 3.),
+                ),
+                (
                     Text2d::default(),
                     Transform::from_xyz(0., STICK_BOUNDS_SIZE + 2., 4.),
                     Anchor::BottomCenter,
                     TextWithAxes { x_axis, y_axis },
-                    ))
+                    children![
-                    .with_children(|p| {
+                        (TextSpan(format!("{:.3}", 0.)), style.clone()),
-                        p.spawn((TextSpan(format!("{:.3}", 0.)), style.clone()));
+                        (TextSpan::new(", "), style.clone()),
-                        p.spawn((TextSpan::new(", "), style.clone()));
+                        (TextSpan(format!("{:.3}", 0.)), style),
-                        p.spawn((TextSpan(format!("{:.3}", 0.)), style));
+                    ]
-                    });
+                ),
-                // cursor
+                (
-                parent.spawn((
                     meshes.circle.clone(),
                     materials.normal.clone(),
                     Transform::from_xyz(0., 0., 5.).with_scale(Vec2::splat(0.15).extend(1.)),
@@ -321,8 +305,9 @@ fn setup_sticks(
                         scale: STICK_BOUNDS_SIZE,
                     },
                     ReactTo(button),
+                ),
+            ],
         ));
-            });
     };
 
     spawn_stick(
@@ -347,16 +332,15 @@ fn setup_triggers(
     materials: Res<ButtonMaterials>,
 ) {
     let mut spawn_trigger = |x, y, button_type| {
-        commands
+        commands.spawn((
-            .spawn(GamepadButtonBundle::new(
+            GamepadButtonBundle::new(
                 button_type,
                 meshes.trigger.clone(),
                 materials.normal.clone(),
                 x,
                 y,
-            ))
+            ),
-            .with_children(|parent| {
+            children![(
-                parent.spawn((
                 Transform::from_xyz(0., 0., 1.),
                 Text(format!("{:.3}", 0.)),
                 TextFont {
@@ -364,8 +348,8 @@ fn setup_triggers(
                     ..default()
                 },
                 TextWithButtonValue(button_type),
+            )],
         ));
-            });
     };
 
     spawn_trigger(-BUTTONS_X, BUTTONS_Y + 145., GamepadButton::LeftTrigger2);
@@ -374,8 +358,7 @@ fn setup_triggers(
 
 fn setup_connected(mut commands: Commands) {
     // This is UI text, unlike other text in this example which is 2d.
-    commands
+    commands.spawn((
-        .spawn((
         Text::new("Connected Gamepads:\n"),
         Node {
             position_type: PositionType::Absolute,
@@ -384,8 +367,8 @@ fn setup_connected(mut commands: Commands) {
             ..default()
         },
         ConnectedGamepadsText,
-        ))
+        children![TextSpan::new("None")],
-        .with_child(TextSpan::new("None"));
+    ));
 }
 
 fn update_buttons(