Teach them to love and respect the environment
You should talk to your kids about loving and preserving nature, read interesting books on this topic to them, go hiking once in a while to show them all the beauty of nature, etc. At a young age, kids absorb information very easily, remember that.
Recycle with your kids
Teaching your kids about recycling is also very important. They should understand from the young age what is trash and what can be recycled. Make recycling a regular and fun routine for you and your kids. Let them get used to it and see it as the only way there is.
Tell them about waste and overconsumption
Your kids should realize that it is important to save water (ask them to turn it off when they are brushing teeth, for example), energy (turn off the lights when leaving a room), food (overeating is always a bad idea), etc. Make sure you teach them to take only what they need and not to be greedy.
Protect them from harmful information
Of course, you cannot hide the fact that there is violence and cruelty in this world. However, everything is good in its season. And your eight year old, for example, doesn't have to watch videos with people being beaten or animals being hurt. Kids are all online these days, you cannot escape from it. Apart from the useful things they search there, they can also see (accidentally or intentionally) inappropriate and harmful content. Such content can really hurt their young spirit. So, you should protect your children from it by limiting their Internet use or blocking inappropriate sites with software like https://pumpic.com/. Don't let negative information influence your child's view on life.
Walk and ride a bike
Saving environment by not driving a car is also important. You often cannot do without it at all, but when you have some more time, ride bikes with your kids or take a walk. Go to a nearest store by foot or ride a bike to a close park and have a picnic there. It is a great thing for your kid's health and mind.
Make a small garden together
You can involve your kids in a fascinating activity - growing plants, fruits, vegetables and flowers. If you don't have a garden, you can simply grow some flowers in a pot. Also it can be helpful to take your kids to some local farm so that they see how everything works. You can tell them about the importance of organic food when you go on this trip.
There are many other ways how to raise green awareness in your kids. You can also use recyclables for crafting, carry re-usable bags with your kids, do volunteer work together, etc. Be creative and you will raise great kids with green approach to life.