If you have been using iCloud and are making the switch to use the local backup option it should be a fairly quick and easy switch. If you have issues are not seeing the option to use iTunes here are some things to check.
Please click on the Cog button after selecting your child and then click on Data Connections
If you show the Red REMOVE ACCOUNT as shown below please select it. This will remove the current connection and allow you to make a new one to iTunes.
You will then have a second button to Confirm you wish to Remove the login credentials.
You will be taken back to the main child profile at this point. You can now again go to the Data Connections and complete the setup to itunes.
Here is a great article that will you step by step through the locoal backup process.
Local Backup Setup and Connection
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