The App is Free-to-download, but provides access to only 20% of all questions and all features except premium features such as Topical Exercises and CA/SA upon initial download.
For the Child, there will be faster game progress (shorter building construction time and increased resource harvesting) with an active subscription.
Subscription is available in the form of 1-month ($3.98), 6-months ($21.98) and 12-months usage ($36.98), and auto-renewals.