So yesterday and today I played through Snowyhill and most of The Wintery Base (I missed two of the keychains). They were pretty good for first attempts! I imagine as they play through more worlds by others they'll get a hang of some of the conventions (The Wintery Base had some secret levels inside secret levels, I think, which was kinda weird, and also going over 30 levels is a bit much, but thankfully most of them were pretty short). Feel free to post more of your (or your kids') worlds as you make them!
Anyways, I think the reason it never became a massive success was probably due to a lack of advertising and the fact that Indie games didn't really get a fair platform to compete with major industry games until the last couple years. By then, it wasn't so new anymore. But hey, if you tell your friends/family about it (get some good word of mouth), since it's free there's an incentive to at least try it!
I don't know if I'll be making any worlds anytime soon, but maybe in the next couple months. I'll be checking these boards every now and then, so again, if you post any more worlds, I'll see them and get around to playing them at some point!