Unfortunately, according to App Store rules, you cannot share in-app subscriptions through Family Sharing.
However, you can share your subscription across multiple devices using the “Sign-in” feature.
To share your subscription on another device, please follow the steps -
Open Kiddopia on the device that you purchased it.
Tap on the Settings icon.
Here tap on Sign In and follow the instructions.
Once you have signed in, please follow these steps on the devices that you’d like to share the app using the same account to sign in that you used above.