I've found that including children in the process of reusing and upcycling everyday items has been a fun way to teach them about eco-friendliness.
For example, my child helps me sort our plastic bags into different colors for recycling. We also wash and save our glass jars and decorate them to store things like buttons, or we use them for drinking glasses. It's become a bit of a game for my little one to spot how many ways we can reuse these jars!
Another thing we do is make our own play dough with flour, salt, and water - such a simple but fun activity and no nasty chemicals. Kids love the satisfaction of squishing it all together and it keeps them entertained for hours. And of course, an added bonus is that there's no plastic packaging waste like you get with store-bought play dough.
I'd love to hear other people's ideas too!