"I have a parent page that uses 'use client'"
better not mark your page.tsx as "use client"

"Both have 'use client' on top,"
adding "use client" to the top does a little more than just "marking" your component as client component. it is actually also marking your component as the gateway/boundary from server -> client. As such, all components that are marked with "use client" will be checked if they have any functions or unserializable props passed to them. As a result, passing a setState (or any function in that regard) is illegal unless you are trying to make "Server Actions" (which is what the error suggests, by adding "use server").

I want the entire page to be client side rendered because there is state being managed at the top

'use client';
import { useState } from 'react';

export default function Page() {
    const [a, setA] = useState('');

    return (
        <>
            <Child a={a} setA={setA} />
            <Child2 a={a} />
        </>
    );
}

so for a page like this, how would it work?

just use "use client" at the top of the tree where you dont pass any function

yea one way of doing this is by just creating a component like

export default function Page() {
  return <PageClient />
}

that way you dont use "use client" at page.tsx

I see, I guess I can do that

use "use client" where you clearly define, "Hey this is the front-line/front-gate where server meets client"

actually nvm I found my issue, it was apparently my layout file that needed use client instead, it just didnt tell me that was the problem and directed me to the page for the error...

thats even worse 😭

but okay

I dont even use any function calls in the layout, but I am using a ui library

okay, im just saying that usually its not good practice to put "use client" in layout.tsx or page.tsx

why?

yeah ik, but I need it to manage state and its a pretty lightweight app

if the page is entirely client side, it's fine.

i suspect the question is a bit flawed though. you likely want to use context to share state between siblings https://react.dev/reference/react/useContext

it was shown to have unexpected results in the past

maybe it is more stable now