When I was around that age I was very enthused to encounter the book Origami in Action by Robert Lang at the local library. There are plenty of beginner-friendly models to start with, but also some cool complex models that will spark wonder and possibly ignite the motivation to practice and improve. Jeremy Shafer's Origami to Astonish and Amuse similarly has a range of easier and tougher models, comparatively slanted a touch more towards the complex. What's great about both of these books is they have a strong focus on interactive models towards which kids would likely gravitate, compared to books by, say just for example, John Montroll, which while definitely engaging, adhere to a more representational tradition. Both books are available on Amazon. For paper I think a good starting point would be 10 inch kami like this. That would serve well for a majority of what's in the Lang book. Some of the more complex models in the Shafer book would benefit from foil like this. Of course that would most likely be further down the line but with just those two books and a couple sets each of that paper you've opened up a lot of runway for the hobby to really take off.