diff --git a/src/myfasthtml/controls/Boundaries.py b/src/myfasthtml/controls/Boundaries.py
index f82ac89..d85c3c2 100644
--- a/src/myfasthtml/controls/Boundaries.py
+++ b/src/myfasthtml/controls/Boundaries.py
@@ -26,10 +26,10 @@ class Boundaries(SingleInstance):
   Keep the boundaries updated
   """
   
-  def __init__(self, owner, container_id: str = None, on_resize=None, _id=None):
-    super().__init__(owner, _id=_id)
-    self._owner = owner
-    self._container_id = container_id or owner.get_id()
+  def __init__(self, parent, container_id: str = None, on_resize=None, _id=None):
+    super().__init__(parent, _id=_id)
+    self._owner = parent
+    self._container_id = container_id or parent.get_id()
     self._on_resize = on_resize
     self._commands = Commands(self)
     self._state = BoundariesState()
diff --git a/src/myfasthtml/controls/Panel.py b/src/myfasthtml/controls/Panel.py
index aa959ee..8223f1b 100644
--- a/src/myfasthtml/controls/Panel.py
+++ b/src/myfasthtml/controls/Panel.py
@@ -104,7 +104,7 @@ class Panel(MultipleInstance):
   the panel with appropriate HTML elements and JavaScript for interactivity.
   """
   
-  def __init__(self, parent, conf: Optional[PanelConf] = None, _id=None):
+  def __init__(self, parent, conf: Optional[PanelConf] = None, _id="-panel"):
     super().__init__(parent, _id=_id)
     self.conf = conf or PanelConf()
     self.commands = Commands(self)
diff --git a/src/myfasthtml/controls/Profiler.py b/src/myfasthtml/controls/Profiler.py
index 4b87e20..71cb7ae 100644
--- a/src/myfasthtml/controls/Profiler.py
+++ b/src/myfasthtml/controls/Profiler.py
@@ -161,7 +161,7 @@ class Profiler(SingleInstance):
   
   def __init__(self, parent, _id=None):
     super().__init__(parent, _id=_id)
-    self._panel = Panel(self, conf=PanelConf(show_right_title=False, show_display_right=False), _id="-panel")
+    self._panel = Panel(self, conf=PanelConf(show_right_title=False, show_display_right=False))
     self._panel.set_side_visible("right", True)
     self._selected_id: str | None = None
     self._detail_view: str = "tree"
diff --git a/src/myfasthtml/core/instances.py b/src/myfasthtml/core/instances.py
index 6c4c91f..74774be 100644
--- a/src/myfasthtml/core/instances.py
+++ b/src/myfasthtml/core/instances.py
@@ -1,3 +1,4 @@
+import inspect
 import logging
 import uuid
 from typing import Optional, Literal
@@ -32,9 +33,15 @@ class BaseInstance:
     if VERBOSE_VERBOSE:
       logger.debug(f"Creating new instance of type {cls.__name__}")
     
-    parent = args[0] if len(args) > 0 and isinstance(args[0], BaseInstance) else kwargs.get("parent", None)
-    session = args[1] if len(args) > 1 and isinstance(args[1], dict) else kwargs.get("session", None)
-    _id = args[2] if len(args) > 2 and isinstance(args[2], str) else kwargs.get("_id", None)
+    sig = inspect.signature(cls.__init__)
+    bound = sig.bind_partial(None, *args, **kwargs)  # None pour 'self'
+    bound.apply_defaults()
+    arguments = bound.arguments
+    
+    parent = arguments.get("parent", None)
+    session = arguments.get("session", None)
+    _id = arguments.get("_id", None)
+    
     if VERBOSE_VERBOSE:
       logger.debug(f"  parent={parent}, session={debug_session(session)}, _id={_id}")
     
diff --git a/tests/core/data/conftest.py b/tests/core/data/conftest.py
index a36a1ce..a08cc19 100644
--- a/tests/core/data/conftest.py
+++ b/tests/core/data/conftest.py
@@ -41,4 +41,4 @@ def db_manager(parent):
 
 @pytest.fixture
 def dsm(parent, db_manager):
-  return DataServicesManager(parent, parent._session)
+  return DataServicesManager(parent)