A good classroom resource that I found to teach students about strong password creation is this Trend Micro Cyber Academy lesson activity: https://www.trendmicro.com/internet-safety/for-kids/cyber-academy/how-to-create-strong-passwords

It would be good for the Year 7/8 level and contains a short video on password creation and what makes a good password.  It also provides a conversation guide to help the teacher discuss this in class and references the video.

Lastly, there is a Kahoot quiz that reinforces what defines good and bad passwords.