I play with my nephew and nieces (ages 6-13)
As always, start with the wild sheep chase.
Let them choose their “play style.” Do they want to cast spells like Elsa? Shoot bow and arrow like in Tangled? Do the want to sneak around and thief like Aladdin?” Kids above ten can have more specific choices, but under that you’re better off just making their characters for them.
I don’t describe combat as vividly, but as all kids they love funny role play voices by NPCs. They’ve got great imaginations to help them see what you’re describing.
I also just give them basic dice rules. “This is your d20, you use this first all the time. This is your d8, put it right here on your character sheet next to the name of the weapon, you only pick up this dice when it’s time to use the weapon.” As long as they have basic addition down, they get along fine.