There are some very fun and educational games on the blockly website. The reason I find them fun is because they involve a challenge, problem solving and critical thinking. I believe that students who enjoy a challenge would find the task quite engaging, however students who experience low motivation, low self-esteem and/or need lots of support might need extra help and encouragement.
Some links to the curriculum might be:
(Year 5 Technologies) Data is represented using codes (ACTDIK015)
Students could simply have some self-guided fun, there is a lot of choice in terms of games available and the various levels. To add some more structure, students could share what they learnt about the way that their code can represent information. They could also use this as an introduction to writing their own code from scratch (with no pre-existing code) and as an extra challenge, explore the other code language – java.