I tried to get into fly fishing when I was around 12 with a kit rod and it was terrible. That thing set me back years. I didn't get back into it until after my senior year of high school when I decided to get a Scott A2 before going to school Bozeman. It isn't a flashy rod, but it gave me a solid tool with which I was able to teach myself how to fly fish. That springboarded into a lifelong passion for me that is equal to my passion for hunting.
If you end up going with a kit rod, I would go with something trusted like the Echo Traverse or Orvis Clearwater kits. I haven't personally messed with these rods, but I do know that Kelly Galloup (well known fly fishing innovator) had a video on an Echo kit rod and his shock at just how good it was. It does sound like these kit rods are dramatically better than the crap I tried to start with 20 years ago. You can even get into these kits now for less than I paid for my introductory model Scott rod, a Redington reel and Rio fly line when I bought them new in 2009, and that isn't even considering inflation. You can also look a little higher up the scale, but I think that might be too many variables. By getting a good kit rod you will eliminate a lot of choices (fly line brand, fly line taper, reel brand and model) that are just noise for a beginner.
The best thing you could do is to practice casting in your yard. When I got my first rod the guy in the fly shop gave me a 20 minute casting lesson. I then had 3-4 30 minute casting sessions in my yard before I even went fishing. With the proliferation of excellent instructional content on YouTube and the ability to easily film yourself casting with a cell phone, there hasn't been a better time to learn how to cast. You practice shooting a rifle or a bow, so why wouldn't you practice how to cast your fly rod?
If you are looking for good stuff on YouTube, I think the best informational content is produced by the fly shops. The channels I would look at are The Slide Inn (Kelly Galloup's fly shop), Fly Fish Food (Cheech, Curtis and Lance, lots of fly tying content and they have a fly fishing skill builder series), Red's Fly Shop (lots and lots of educational content covering many different ways to fish), Charlies Fly Box (Charlie Craven's fly shop, lots of fly tying and fly fishing discussion), and Jensen Fly Fishing (married Canadian couple associated with Orvis that have lots of educational content). Yeah, unlike Randy's show these fly fishing channels are often directly associated with businesses instead of just sponsored by the business. But educational content has been the standard practice for any good fly shop I have ever been in, whether or not they are on YouTube. I think these are channels are all kid friendly except for maybe the names of some of Kelly Galloup's fly patterns, but in a few years your kid will probably be chuckling at the double entendres.