diff --git a/src/suou/sqlalchemy.py b/src/suou/sqlalchemy.py
index 5490ecb..0245ed6 100644
--- a/src/suou/sqlalchemy.py
+++ b/src/suou/sqlalchemy.py
@@ -194,7 +194,7 @@ def age_pair(*, nullable: bool = False, **ka) -> tuple[Column, Column]:
     return (date_col, acc_col)
 
 
-def parent_children(keyword: str, /, lazy='selectin', **kwargs) -> tuple[Incomplete[Relationship], Incomplete[Relationship]]:
+def parent_children(keyword: str, /, *, lazy: str = 'selectin', **kwargs) -> tuple[Incomplete[Relationship], Incomplete[Relationship]]:
     """
     Self-referential one-to-many relationship pair.
     Parent comes first, children come later.