Someone asked in another thread and only suggestion was sellotape at the rear of TRV
Unless Tado can do it. I've learned over the years that there are plenty configuration settings available to them not surfaced to customers. Couldn't say if that is one though.
In settings for the zone, set the action to timer with a value of 00:01.
Of course child-lock was a feature that they had on their roadmap years ago but didn't bother implementing...