If you want to introduce young children to TTRPG, buy Hero Kids now. Look no further, you've found what you need.
My oldest son, now in 3rd grade, having observed parts of the monthly D&D game I DM, asked if he could play D&D. While he is mature enough that I could create some appropriate adventures, his younger brother is in kindergarten and I know he is not ready for D&D. I've noticed Hero Kids in the past so I decided to give it another look. They had a bundle with the core rules, all expansions, and all adventures to date for only $15 and that also came with a discount on the printed version of the rules. I bought it, and ordered a print copy of the rules, immediately.
I probably didn't need to order the print book. I read the PDF rules in one short sitting. They are easy to pickup. Still, it will be nice to have a print copy to refer to and for my boys to use for running their own games.
I ran the first adventures, Basement O' Rats, last night. This is the intro "easy" level adventure. My boys were able to get through without any knock-outs (like Pokemon, nobody "dies", they are KO'd). We used the pre-created characters, but after the game they wanted to make their own, so they ended the evening writing up and coloring new characters they made up.
They wanted to play again, so today I ran Escape from the Ghost Pirates. It was "normal" level and was a good challenge for them. Enough to keep them on the edge, but not so hard that they were overly frustrated. It was great to see my two boys learn that they had to work together to succeed and to watch them learn to take time to plan their next steps.
All adventures come with battlemaps and paper minis and stat cards for any new monsters. All you need to do is print them out and obtain six-sided dice and pencils. The encounters for each adventures suggest the number of monsters based on the number of heroes, including only one hero. You can play this with just one kid, no problem, and it will still be fun.
The expansion packs given you additional pre-gen heroes to chose from and special equipment that the game master can give out as loot.
After the second adventure, my 10-year old asked if he could create his own dungeon. He roughed out a simple map on graph paper, which I turned into a number of battlemaps in Dungeonographer and he created a new monster (mole men) for it. So this evening, he'll be DM running his adventure for his brother, my wife, and I.
I do not see my 10-year-old being able to pick up D&D and run a game, certainly not after only two games. To me, this is Hero Kid's brilliance. It is is a well-balanced, simple to learn system, requiring a minimum of investment, but all the TTRPG fundamentals are there. It is a fabulous introduction to TTRPGs for children.
My only complaint is that if you want to create your own adventures, the rulebook doesn't provide any guidance for creating monsters and there are not blank monster cards or blank paper-minis. We just used the cards and paper minis that are used to create your own heroes and pretty much winged it in terms of creating stats for homebrew monsters, using RAW monsters as templates.
This game really needs to be put into a boxed set and sold in Target. I think it is one TTRG that would easily be attractive and adopted by mainstream families. If I could buy this in a box set, I would be giving it as a gift to every young kid I know who doesn't have it.