DragonBox is giving them a sense of familiarity and comfort-level and ownership of algebra-world. That can only be a good thing when they start doing algebra for real.

I completely understand! I am a huge fan of the book "Introductory Calculus for Infants", I realize that most people who have seen it think it is a joke. It's basically an ABC's book, but it gives exposure to the ideas of graphing, formulas, planes, etc. It makes the symbols less scary (plus it's pretty funny to listen to a pre-schooler rattle off the pdf of the normal distribution).

We are a relatively mathematical household, so we have a ton of incidental exposure. But I leave the connections and the logic to my DD since that's really what math is. We also have a few books in the Sir Cumference series which she finds hysterical. I feel at this age exposure to the symbols and the nomenclature of math allows children the ability to overcome that initial fear (Since it does resemble a foreign language). Allowing them the ability to express it in terms of logic and connections and the underlying art form that it actually is.