Thanks for your comments. We have been letting the kids have their own fire for quite some time now. The first 2-3 camping trips, they rubbed sticks for hours! And they gathered wood for quite some time too. What a great way to keep them busy. That showed me they were serious, so then I showed them how to actually start it. They get lots of whitish powder from rubbing the sticks the wrong way. I told them they need a darker powder from friction. Then I let them use a ferro rod. They LOVE that!

Then they learn to keep their fire going even if they let it burn down a bit by fanning the coals.