reflex-dev/reflex · error · TypeError

`children` in `{fn_name}` cannot be `rx.RestProp`.

Error message

`children` in `{fn_name}` cannot be `rx.RestProp`.

What it means

An `@rx.memo` function declared a parameter named `children` annotated as `rx.RestProp` (the `...` rest-props placeholder). The `children` slot is special — it maps to React's children — and cannot double as the catch-all rest-props bag. Reflex raises this TypeError during parameter validation at decoration time.

Source

Thrown at packages/reflex-base/src/reflex_base/components/memo.py:944

def _validate_children(
    parameter: inspect.Parameter, fn_name: str, for_component: bool
) -> None:
    if parameter.name != "children":
        msg = (
            f"`rx.Var[rx.Component]` parameters in `{fn_name}` must be named "
            "`children`."
        )
        raise TypeError(msg)


def _validate_rest(
    parameter: inspect.Parameter, fn_name: str, for_component: bool
) -> None:
    if parameter.name == "children":
        msg = f"`children` in `{fn_name}` cannot be `rx.RestProp`."
        raise TypeError(msg)


def _validate_event_trigger(
    parameter: inspect.Parameter, fn_name: str, for_component: bool
) -> None:
    if not for_component:
        msg = (
            f"`rx.EventHandler` parameters are only supported on component-"
            f"returning memos. Got `{parameter.name}` in `{fn_name}`."
        )
        raise TypeError(msg)
    if parameter.name == "children":
        msg = (
            f"`children` in `{fn_name}` cannot be an `rx.EventHandler`; "
            "use `rx.Var[rx.Component]`."
        )
        raise TypeError(msg)
    if parameter.default is not inspect.Parameter.empty:

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Rename the RestProp parameter to something else (e.g. `rest: rx.RestProp` or use bare `...` on an unnamed slot) so `children` stays free
2. Declare `children: rx.Var[rx.Component]` separately if you need the children slot, and use a differently-named `rx.RestProp` for extra props

Example fix

// before
@rx.memo
def panel(children: rx.RestProp) -> rx.Component:
    ...

// after
@rx.memo
def panel(children: rx.Var[rx.Component], rest: rx.RestProp) -> rx.Component:
    ...

import inspect, reflex as rx

def check_no_rest_children(fn) -> None:
    for p in inspect.signature(fn).parameters.values():
        if p.name == "children" and p.annotation is rx.RestProp:
            raise TypeError("children cannot be rx.RestProp; rename the rest param")

import inspect, reflex as rx

def is_valid_rest_usage(fn) -> bool:
    return all(
        not (p.name == "children" and p.annotation is rx.RestProp)
        for p in inspect.signature(fn).parameters.values()
    )

When it happens

Trigger: Writing `def my_memo(children: rx.RestProp)` (or `children: ...` where RestProp is the annotation) so `_validate_rest` sees `parameter.name == "children"` and raises.

Common situations: Trying to forward all props including children with a single rest parameter and naming it `children`; auto-generating memo signatures from `**kwargs` and accidentally colliding with the reserved name.

Related errors

• `rx.Var[rx.Component]` parameters in `{fn_name}` must be nam
• `children` in `{fn_name}` cannot be an `rx.EventHandler`; us
• `children` in `{fn.__name__}` must be annotated as `rx.Var[r
• `@rx.memo` only supports one `rx.RestProp` in `{fn.__name__}
• Var-returning `@rx.memo` `{func_name}` cannot depend on embe

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/b7caf0275c6dc41e. Report an issue: GitHub.