Don’t do it.
Seriously, my son Mac has been pestering me for ages to run Pathfinder for him because he occasionally reads OotS (missing the blue humor) and liked the idea of paladins summoning animals, something that doesn’t happen in Fourth Edition D&D. I should have, in retrospect, pushed Castles & Crusades with some scratchbuilt rules about alternatives mounts, but Pathfinder had the slick art and whatnot so after being worn down by constant pestering I finally caved and ran a session.
After three rooms, the kids and I were all sick of it.
When you’re nine, you want everything to go your way, you want to be able to win after an appropriate amount of effort, you don’t want to keep track of Armor Checks and skill modifiers. What Mac and his friend did was just go put on capes and toy swords and use their imagination instead, which was fine with me.
I get the game isn’t for children, and I understand why. But I’m also aware that teaching the damn game was a pain in the backside, and afterwards Mac came up to me and said, “next time, let’s do Labyrinth Lord.”