You are not able to turn off Two-Factor Authentication.
https://support.apple.com/en-us/HT204915
"If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, you can unenroll within two weeks of enrollment. Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure and means that you can't use features that require higher security."
If you want to check the location of your children's device you can setup Family Sharing and remained signed into your own Apple ID to locate it. https://support.apple.com/en-us/HT201088