We played a game of "giving instructions".
At the start of the game each child has built a small model of an animal using no more than 20 lego pieces.
Then children sat back to back in pairs. One was to give verbal instructions only about how to build his/her model. The other child did not see the original model and had to build from the instructions only.
The goal is to build a model that is as close to the original as possible.
It is a very difficult, almost impossible task even for adults and even if you know the names of all lego parts.
So the more practical goal was to experience a situation where a certain language and precise instructions are required. It is somewhat related to computer programming (something that we are trying to learn) where very specific instructions are to be given to a computer in a special language.
Here are some of the original and "matching" models. Some models are exact copies. I guess when children became frustrated with inability to explain - they "optimized" and stepped over the game rules, but it was still fun and useful.