I am amazed that with so many successful programs out there your question doesn't have hundreds of suggestions or ideas posted.
First to answer your last question, yes the program should be different depending upon the age group. I would even suggest that K thru 2 is more of a reasonable cutoff, and then 3rd through 5th, 6th through 8th. Older than that I think you start dealing with specifics i.e. work related, personal... such as home and health, and than environmental.
But as to your needs for your department. I think when you are dealing with the K to 2 group remember they have a short attention span and their learning curve lends itself toward repetition. Teach them what to do if their clothes catch fire (Stop,Drop and Roll) the firefighter should demonstrate and then get some of the students to repeat the firefighters actions. The phrase Stop, Drop and Roll sounds like a rhyme and they will repeat it often. Teach them that matches are tools (for grown-ups) not toys. Make sure they understand when they find them to give them to an adult. If they grasp those two lessons and you can quiz them during the live demonstration as to the correct responses, you will have made an impact.
3rd through 5th are hungry to learn things, it makes them feel important. Take a blanket with you and have you and the teracher or another firefighter stretch the blanket out between you and hold it about three feet from the floor. Have the students crawl under it and explain that this is the level smoke could be if their house was on fire. Explain how smoke and heat rises and cooler, breathable air is near the floor. Teach them about calling 9-1-1 or the local emergency number for fire response. The need to know their address, phone number and to call from a safe location, not their house if its on fire. Discuss meeting places out side their home for the whole family etc. This can all be done in 30 minutes and you can evaluate their knowledge of the subject by asking questions of the class or asking them to demonstrate.
6th through 8th like visuals with data. I would use tools that are easily transportable like empty gasoline containers and explain how fuel vapors work. Appliances like coffee pots, pots and pans and the need to move handles inward so they cannot be bumped by elbows or arms. Burn prevention items and what to do when you sustain one (cool a burn). We speak about bath water temperatures, microwaves, metal objects heated by the sun etc.
If it would help see if someone in you area has an old copy of NFPA's Learn Not To Burn. It was developed in age appropriate manuals. On line their are several free sources. The Lowes Home Safety Council has free material, Safe Kids Coalition has some injury prevention tools.
Good luck it is the most important work you do as a firefighter. You can save more lives with prevention then a hose. No offense to all of us in the service, but teaching them what to do in case of fire, or how to prevent them from ever occurring is true life saving work.