No they don't grow. They stay elementary. What is missing from my simplified equation is the energy released in the reaction. As I was saying to @justtryme90 here above, this energy is crucial with respect to the dark matter behavior in the universe history.

At some point, the 3 to 2 process will stop to be effective and only the 2 to 2 one will be left. And a bit later, all processes will stop and the dark matter density will freeze out.