I can't think of any way to guarantee getting a child excited about programming.
But if I were coming up with a list of places not to start, ideas of what adults think ought to be fun would be on it. So would sitting down.
Anyway, I will give making a list of positive stating points a shot.
() It is a long term project. The kid has been around computers and knows they make pictures. There's no way to make a miracle moment for an 8 year old. They've seen an iPad.
() Focus on the young adult ten years away, not trying to create a HN front page prodigy.
() The interesting part of programming, and the part about which we are passionate is not the typing. It is the ideas.
() What children love is being taken seriously and learning. The best way to do this is by removing the shiny screen from the equation and having a conversation - give them words to add to their vocabulary and ideas by which to see patterns in the world.
() Be present. Throw a ball or kick one and instead of lecturing on technique, talk about what computers can do. Only sit down at a screen if you are asked to demonstrate. It's got to be natural...come to think about it, going for a walk is a good approach.
Plans to get a child excited about x are pretty much analogous to the management methods of the PHB.
Sharing your passion is great. But it's your passion not the child's. Maybe some of it will rub off and a seed will be planted. But it is a seed. It needs to be given time and space to grow and though it may produce a mighty oaken programmer, the odds are the child will grow to a maple or dogwood or redwood or beanstalk.
And the only healthy approach is to go into the relationship being ok with that.
After we played around a bit with the editor we checked out games that others had made, and the kids were super excited when they realized they could actualy build the games they had played themselves.
I'd let him/her play around in Scratch a bit, show some existing projects, and then build a game/project together from their interests (which is roughly what we do in our class).
He asked me "How do I use it?" I told him that I didn't know, and that he should watch the tutorials. An hour later I came back and he had made a game where all the characters attacked each other automatically. He showed me how he chose the characters responses (if this happens, then do that). I thought it was pretty cool. I still don't know how to use the software, but he has made a bunch of little games.
I got into programming partly learning how to program, but also experimenting by hacking up BASIC games, it was fun to change the rules, and or actions in the game, and energized my desire to learn to write my own.
If that doesn't get him interested he's probably never going to get interested.
A fun easy framework for game-making is LÖVE. https://love2d.org/ You can show the kid some games made using LÖVE (https://www.love2d.org/wiki/Category:Games), do some of these tutorials (https://www.love2d.org/wiki/Category:Tutorials)...
Even if you don't know Lua, it's so easy to pick up (http://learnxinyminutes.com/docs/lua/). And figuring out a new language with the 8 yr old could be cool too.