mark children apis as unstable

Author: jayshrivastava

datafusion/physical-expr/src/expressions/dynamic_filters.rs

@@ -382,12 +382,18 @@ impl DynamicFilterPhysicalExpr {
     }
 
     /// Return the filter's original children (before any remapping).
+    ///
+    /// **Warning:** intended only for `datafusion-proto` (de)serialization.
+    /// Not a stable API.
     pub fn original_children(&self) -> &[Arc<dyn PhysicalExpr>] {
         &self.children
     }
 
     /// Return the filter's remapped children, if any have been set via
     /// [`PhysicalExpr::with_new_children`].
+    ///
+    /// **Warning:** intended only for `datafusion-proto` (de)serialization.
+    /// Not a stable API.
     pub fn remapped_children(&self) -> Option<&[Arc<dyn PhysicalExpr>]> {
         self.remapped_children.as_deref()
     }