By influencing them earlier on, it will become a part of their habit.
Don't make it sound complicated. It's easier for them to understand if you use simple words and examples they can relate to. Start by encouraging them to turn of lights when leaving an empty room, or to turn of the fan when no one is around or when it isn't hot.
Always give gentle reminders and reward them when they do a part in preventing global warming. I believe this method of teaching global warming..
As it is with lights, you may want to explain to them about other appliances in the house. You could start with refrigerator. Teach them to keep the refrigerator door closed whenever they're done with it and to not keep the door open any longer than needed. You should also explain to them that they need to make sure the door is always closed properly or it will use up more energy trying to maintain the temperature inside. Not closing the door properly will cause the cold air to leak out, thus the refrigerator to becomes less cold and for it to be colder the refrigerator will expand more electricity for this.
Again, use simple words so that they understand what you're telling them.
Next you can show them about proper water usage. Have them use a mug when brushing their teeth rather than letting the tap run. Energy is used to purify and heat water that we use on a daily basis.
You should do the same for yourself by turning off the water when brushing your teeth as you want to be a role model for the kids.
Other household related habit that is suitable for teaching global warming for kids can is learning about recycling. Try to teach your kids to recycle all the aluminum cans, glass bottles and newspapers that are no longer needed. Explain to them how recycling actually helps save energy and this helps make Earth cooler.
There are, of course, other things you can teach your kids about global warming. You can also teach them about gardening..
Encourage your kids to use public transportation whenever possible. Every little bit helps!