The kids are so lucky to be given this experience! Long ago, I studied Turkish miniature painting from a Turkish artist. We used Windsor Newton designer’s gouache opaque watercolors. She taught us how to make gold paint from gold leaf, but I agree that it’s too expensive and difficult for kids. Gold paint should be good enough for their first experience. For those who are deeply interested and want to study in more depth, you can teach them the gold leaf technique later.
I still remember spending 10 hours on a small 2 inch by 3 1/2 inch painting using brushes with 3 or 4 hairs. It certainly teaches patience!