diff --git a/lago_python_client/mixins.py b/lago_python_client/mixins.py
index 8b6163d..8c510b5 100644
--- a/lago_python_client/mixins.py
+++ b/lago_python_client/mixins.py
@@ -173,6 +173,7 @@ def find_all(
                 ),
                 query_pairs=options,
             ),
+            headers=make_headers(api_key=self.api_key),
             rate_limit_retry_config=self.rate_limit_retry_config,
         )
 
diff --git a/tests/test_find_all_children.py b/tests/test_find_all_children.py
new file mode 100644
index 0000000..37b25d7
--- /dev/null
+++ b/tests/test_find_all_children.py
@@ -0,0 +1,40 @@
+import pytest
+from pytest_httpx import HTTPXMock
+
+from lago_python_client.client import Client
+
+
+@pytest.mark.parametrize(
+    "client_name,parent_resource,child_resource",
+    [
+        ("customer_applied_coupons", "customers", "applied_coupons"),
+        ("customer_credit_notes", "customers", "credit_notes"),
+        ("customer_invoices", "customers", "invoices"),
+        ("customer_payment_methods", "customers", "payment_methods"),
+        ("customer_payment_requests", "customers", "payment_requests"),
+        ("customer_payments", "customers", "payments"),
+        ("customer_subscriptions", "customers", "subscriptions"),
+        ("customer_wallets", "customers", "wallets"),
+        ("plan_charges", "plans", "charges"),
+        ("plan_fixed_charges", "plans", "fixed_charges"),
+        ("subscription_charges", "subscriptions", "charges"),
+        ("subscription_fixed_charges", "subscriptions", "fixed_charges"),
+    ],
+)
+def test_find_all_children_sends_authentication_headers(
+    httpx_mock: HTTPXMock, client_name: str, parent_resource: str, child_resource: str
+):
+    client = Client(api_key="test-api-key")
+    response_data = {child_resource: [], "meta": {"current_page": 1}}
+    httpx_mock.add_response(
+        method="GET",
+        url=f"https://api.getlago.com/api/v1/{parent_resource}/parent-id/{child_resource}?per_page=2&page=1",
+        json=response_data,
+    )
+
+    response = getattr(client, client_name).find_all(resource_id="parent-id", options={"per_page": 2, "page": 1})
+
+    request = httpx_mock.get_request()
+    assert request.headers["Authorization"] == "Bearer test-api-key"
+    assert request.headers["Content-Type"] == "application/json"
+    assert response == response_data