OK, so my passion is Friction Fire, but I thought I would mention the Fire Steel (aka Ferro rod. I don't really like the Ferro rod as it is a modern invention and the hot sparks are actually very hot metal shards. The Ferro rod is a very common bushcraft tool and can be a good way to teach fire lighting before moving onto Friction Fire. Kid's do like Ferro rods due to the sparks but as always with kids and fire you need to teach them to be safe as Ferro rod sparks can hurt and cause things to catch fire!
A fire steel is a modern take on the flint, and consists of a Ferrocerium rod which is a man-made metallic material that produces hot sparks at temperatures of about 3,000 °C (5,430 °F) when scraped against a piece of steel. A fire steel usually comes with a metal striker but you can use the back of a knife as well - do not use the knife blade as it will damage and chip it. Ferrocerium is used in many applications such as cigarette lighters.
So I don't really encourage use of Fire Steels but they are fairly easy to use. You need to hold the rod firm, and point the rod towards the tinder , angle the striker about 30-45 degrees on the rod and push it down the rod applying pressure , and direct the sparks onto tinder It can be a very quick way and very useful in survival situations.
Please do use common sense when introducing children to fire lighting and teach them about fire safety, and always ensure they are supervised when fire lighting and around fires. It is a good idea to have a safe zone around a fire, marked out with sticks. Also, the sparks produced from a Fire Steel are very HOT metal shards and can burn skin and catch things alight (e.g. tents) so children should be supervised when using them.