My bet is that it's MIT's Scratch. Notsomething used in production, but if you have a kid learning how to program these days, it's the obvious good choice (and I've done a ton of research).

The language itself is surprisingly pleasant to program (even for a professional programmer). The real problem is the lack of data structures (like a dict), so some projects (unfortunately, many my 7yo comes up with) become extremely annoying to program.