diff --git a/src/idom/client/app/packages/idom-client-react/src/index.js b/src/idom/client/app/packages/idom-client-react/src/index.js
index e5cc53bc0..d18d406ea 100644
--- a/src/idom/client/app/packages/idom-client-react/src/index.js
+++ b/src/idom/client/app/packages/idom-client-react/src/index.js
@@ -66,7 +66,7 @@ function ImportedElement({ model }) {
       model.importSource.source
     );
     eval(`import("${importSource}")`).then((module) => {
-      mountImportSource(module, mountPoint.current, model, config);
+      mountImportSource(mountPoint.current, module, model, config);
     });
   });
   return html`<div ref=${mountPoint} />`;
@@ -137,21 +137,26 @@ function eventHandler(sendEvent, eventSpec) {
   };
 }
 
-function mountImportSource(module, mountPoint, model, config) {
-  const mountFunction = model.importSource.hasMount
-    ? module.mount
-    : (element, component, props, children) =>
-        reactDOM.render(
-          react.createElement(component, props, ...children),
-          element
-        );
-
-  const component = module[model.tagName];
-  const children = elementChildren(model);
-  const attributes = elementAttributes(model, config.sendEvent);
-  const props = { key: model.key, ...attributes };
-
-  mountFunction(mountPoint, component, props, children);
+function mountImportSource(element, module, model, config) {
+  if (model.importSource.hasMount) {
+    if (model.children) {
+      console.error("Mount function does not support children");
+    }
+    module.mount(
+      element,
+      module[model.tagName],
+      elementAttributes(model, config.sendEvent)
+    );
+  } else {
+    reactDOM.render(
+      react.createElement(
+        module[model.tagName],
+        elementAttributes(model, config.sendEvent),
+        ...elementChildren(model)
+      ),
+      element
+    );
+  }
 }
 
 function useInplaceJsonPatch(doc) {
diff --git a/src/idom/client/module.py b/src/idom/client/module.py
index 0ed138382..09a7eec53 100644
--- a/src/idom/client/module.py
+++ b/src/idom/client/module.py
@@ -129,7 +129,7 @@ def __init__(
     def declare(
         self,
         name: str,
-        has_children: bool = True,
+        has_children: Optional[bool] = None,
         fallback: Optional[str] = None,
     ) -> Import:
         """Return  an :class:`Import` for the given :class:`Module` and ``name``
@@ -147,10 +147,11 @@ def declare(
             raise ValueError(
                 f"{self} does not export {name!r}, available options are {list(self.exports)}"
             )
+
         return Import(
             self.url,
             name,
-            has_children,
+            has_children=has_children,
             has_mount=self.has_mount,
             fallback=fallback or self.fallback,
         )
@@ -183,7 +184,7 @@ def __init__(
         self,
         module: str,
         name: str,
-        has_children: bool = True,
+        has_children: Optional[bool] = None,
         has_mount: bool = False,
         fallback: Optional[str] = None,
     ) -> None:
@@ -192,6 +193,16 @@ def __init__(
                 f"{IDOM_CLIENT_MODULES_MUST_HAVE_MOUNT} is set and {module} has no mount"
             )
 
+        if has_mount:
+            if has_children is True:
+                raise ValueError(
+                    f"Components of {module!r} do not support "
+                    "children because has_mount=True"
+                )
+            has_children = False
+        else:
+            has_children = bool(has_children)
+
         self._name = name
         self._constructor = make_vdom_constructor(name, has_children)
         self._import_source = ImportSourceDict(
diff --git a/tests/test_client/js/vanilla-js-component.js b/tests/test_client/js/vanilla-js-component.js
index 6a9e45687..51e18c7e2 100644
--- a/tests/test_client/js/vanilla-js-component.js
+++ b/tests/test_client/js/vanilla-js-component.js
@@ -1,7 +1,7 @@
-export function mount(element, component, props, children) {
-  component(element, props, children);
+export function mount(element, component, props) {
+  component(element, props);
 }
 
-export function SetInnerHtml(element, props, children) {
+export function SetInnerHtml(element, props) {
   element.innerHTML = props.innerHTML;
 }
diff --git a/tests/test_client/test_module.py b/tests/test_client/test_module.py
index 62d221737..e84b43c70 100644
--- a/tests/test_client/test_module.py
+++ b/tests/test_client/test_module.py
@@ -95,6 +95,21 @@ def test_idom_client_modules_must_have_mount():
     IDOM_CLIENT_MODULES_MUST_HAVE_MOUNT.current = True
     try:
         with pytest.raises(RuntimeError, match="has no mount"):
-            idom.Module("https://some.url", has_mount=False).SomeComponent
+            idom.Import(
+                "https://some.url",
+                "SomeComponent",
+                has_mount=False,
+            )
     finally:
         IDOM_CLIENT_MODULES_MUST_HAVE_MOUNT.current = old_opt
+
+
+def test_no_children_if_import_has_mount():
+    with pytest.raises(ValueError, match="do not support children"):
+        idom.Import(
+            "https://some.url",
+            "SomeComponent",
+            has_children=True,
+            has_mount=True,
+            fallback=None,
+        )