How to migrate child instance creation to Vue 3?

I’m migrating an app from Vue 2.6 to 3.2, currently in migration build, trying to get rid of all the warnings. I can’t figure out how to rewrite the child instance creation.

Current code that successfully mounts the instance/component programmatically under Vue 2:

import ChildComponent from './ChildComponent'
const Ctor = Vue.extend(ChildComponent)
;(childApp = new Ctor({
  router: this.$router,
  store: this.$store
})).$mount()

I tried the following Vue 3 code, it renders successfully, but shows some warnings:

import ChildComponent from './ChildComponent'
childApp = createApp(ChildComponent)
childApp.use(this.$router)
childApp.use(this.$store)
childApp.mount('#child-container')

The warnings:

[Vue warn]: Component "RouterLink" has already been registered in target app.
[Vue warn]: Component "RouterView" has already been registered in target app.

Here is another Vue 3 version of the code that I tried, this one fails to render and displays an error:

import ChildComponent from './ChildComponent'
childApp = createApp({
    router: this.$router,
    store: this.$store,
    render: () => h(ChildComponent),
})
childApp.mount('#child-container')

The error:

Uncaught TypeError: Cannot read properties of undefined (reading '_modulesNamespaceMap')

I'm using the programmatic approach because it allows to preserve the single instance of the component across different layouts that we're mounting it to.

How do I make it to work under Vue 3 without warnings? Thanks!