Thumbturn Child Lock

I designed this simple cover for our internal door lock. In our infinite wisdom (before we had kids) we decided a thumb-turn on our door would be a much easier and quicker solution to opening and locking our door, however since becoming parents, we have quickly realized our little one can work out how to open this!

I didn't want anything to overly complex so i tried keeping it simple, although i have been through 5 iterations but finally found one that seems to work. It's a simple sleeve like design that slides over the thumb-turn preventing it from actually being turned. To hold it in place there is a removable top piece that slides into the sleeve behind the lock mechanism.
I realize this is a potential choking hazard in itself so please be mindful if you do happen to find this design or idea useful.
The top piece is pretty tight so i doubt a little one could remove it easily if at all but you can never be too careful!

It's designed with our lock in mind which i believe i