- Go to the settings
- Find the item "Accounts and synchronization"
- Select "Google"
- At the very bottom click the button "More"
- Select "Delete account"
- Confirm by the button "Delete account"
- Choose a parent account
- Enter the password from the parent's account, click "NEXT"
- Waiting for a few moments
That's all, the child's account from the current phone is deleted.