Hey @7d14709049fd85b4219b0c2249b19d9f,
As you noted, child accounts cannot purchase games, however they can redeem codes that were purchased from an adult account.
This would still be a separate account from your own however, and not currently possible to simply share your copy of the game to a different account.
You can check through more information on those restrictions here, but if you have specific questions related to a game purchase on your account or a child account, please reach out to support so they can take a look at the accounts directly and see what other options may be available.
This thread itself is quite old and will be locked here to avoid further necroposting, thanks!