If your Bosch washing machine has a key symbol on the display and will not start, it means the child lock feature has been activated. To unlock the washing machine, follow these steps:
1. Press and hold the "Start/Stop" button for a few seconds until the key symbol on the display disappears.
2. Press and hold the "Start/Stop" button again for a few seconds until the display shows a flashing "0:01".
3. Release the "Start/Stop" button and the child lock should now be deactivated.
If you are still unable to unlock your Bosch washing machine, you may need to consult the user manual for further instructions or contact the manufacturer for assistance. It is also a good idea to keep the user manual in a safe place for future reference.