The Solvespace UI is a long, long way from being the sort of UI a contemporary kid has any kind of comfort with, I'm afraid, and will be obtuse even to teachers (many of whom, with subjects that concern technology, do not have time to develop expertise in an obtuse UI and may indeed only be confident they understand the meaning of all the lessons they are teaching and not much more).
I don't think bugs in your booleans are your biggest problem at all.
I think Tinkercad has weaknesses as a classic CAD package, and there are things I would like to see done better, but as a package to teach younger people how core concepts in 3D modelling (rather than the ontologies of bRep) actually work, it is the standard you are working against.
which I find a little less confusing than the traditional 3D CAD packages I've tried (and failed to learn) --- at least for Dune 3D I've made it through the tutorial successfully.
Respectfully, I disagree. Even adults have used the word "fun" to describe using solvespace. But I don't actually have feedback from kids, hence the question to OP.
Not saying any of this is easy — Shapr3D on an iPad, expensive and marketed on its extraordinary usability, is just utterly perplexing!
Oh, I actually hate trying to use solvespace with anything other than a 3-button mouse. Unfortunate because the web version can actually run on my phone but is unusable in practice.
I've not used a three button mouse in thirty years. Probably only used a mouse for a dozen hours in the last 15 years.