Consensus rules is how we play all games, in part to address the challenge of other children having learned the "wrong" rules for games. Any rules that are moral, ethical, and safe are allowed, as long as everyone participating agrees on them beforehand. And rules can only be changed mid-game if, again, everyone agrees to the rule change. This also allows for individualized, inclusive rules (e.g., if everyone agrees that the least skilled player -- usually the much younger sibling of someone present -- may play with significantly modified rules, then that is allowed, and they are not considered to be cheating).
Most of the time, though, our collection of board games goes unused, or is repurposed. I think they also prefer games they invent (like trying to land paper airplanes on the ceiling fan (not while it is turning--tried it, doesn't work!)), most of which are noncompetitive.
