Lego is a product primarily marketed to children, yeah, and because of that, many people are only exposed to it in childhood. It makes sense that people would feel infantilized by the introduction of legos if their memories of them are only from childhood. None of this changes the fact that legos are more than capable of stimulating an adult mind on par with their more advanced mental faculties. This is what it means to not be infantilizing. I think there is an issue of harkening to childhood being conflated with infantilization. There is also possibly an issue with how legos are advertised and employed in working sessions, such as in these women-in-tech groups. Putting adults in a room with a bunch of legos without communicated direction or purpose is arguably infantilization. Using legos as a simulation or problem-solving tool with a framed question instead would certainly be effective. Other tools definitely exist which are accessible to adults in the workplace. I suspect legos are chosen out of cheap abundance and to mitigate stress with the nostalgia factor, but this decision is seemingly backfiring in this case. It's quite possible that these thoughts did not motivate the selection, in which case I would definitely agree with the OP that this is all infantilizing. And that's because the legos are not incorporated with purpose, not because legos are somehow childish.