As it turned out the idea with the child particles wasn't that good we ( FreshDumbledor and me ) started to create real multi shots.
Our current state is that you can several shot aprticle systems. Those start at the same time and hit the same target, but can start from different positions ( and all what is possible with 2 different particle systems ).
Things we still think about:
Damage per projectile:
At the current state the damage is calculated for both shots, so two shots, double damage.
At the current state only one splash particle is played back and only one splash damage is calculated.
At the moment there is no way to let the two shots start in different moments ( Imagine a fighter with two guns in his hand shooting with one after another in one animation.)
If we start in different moments, we would need one splash per shot !
Not directly related at the moment, but maybe worth thinking about is "multi attack":
One unit attacks more than one unit at a time.