Command Block help needed

I have a vanilla 1.8.9 server setup in survival mode for my kids. Despite it being survival, I'd like to use command blocks to teleport players to certain parts of the map.

I've changed my server.properties to allow for command blocks (and restarted the server).

My profile is opped to lvl4, and I'm able to run the /give command to acquire a command block. I can place it in the world, but I can't interact with it (to supply it with the intended command), or remove it; right or left clicking does nothing after it's placed.

Anything else I can check?

Thanks for your help guys!