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To save myself from having to write out an essay, I'm just gonna link you to my post on r/rpg about the game Hero Kids. In said post, I also mention 2 other games, the one you mentioned and Amazing Tales (which may be a good fit for you, but I'm not a major fan of it). I'll give you some quick highlights below all the same though. Should be an excellent fit for you!

  • Very easy to learn and get to playing, you can read the book in about an hour and immediately start playing.
    • D6 system working on target numbers.
  • Lots of ready made materials.
    • Adventures (I believe we are up to 13 or so now).
    • Maps and Mini's (paper ones, but that's a plus since your kids can color them).
  • Inexpensive (especially on sale), though I do recommend the "Everything Bundle" which is at an increased cost, but still well within most peoples budgets (~$6 vs ~20).
    • Speaking of the "Everything Bundle", I do mean EVERYTHING past, present, and future!
  • Easily can adjust complexity by adding new elements which can keep the game fresh and interesting. The game grows as your kids do!
    • A happy side effect of this is that if you choose to transition to a system like D&D in the future, this game will allow for that with relative ease.
  • Friendly and helpful community, including the creator who is active in said communities.

The post has a lot more detail and such, so I do suggest you give that a read. If you have any questions please don't hesitate to ask, I'm happy to help! :D