Aiming and Healing...
These are two things I'd like to see improved. Aiming seemed to be stuck to some kind of grid line. However, the kids could move freely. This made aiming a bit difficult, but not too much so.
I noticed that if you upgrade the health, it is fully restored. Later on, after upgrading fully, this becomes a frustrating thing. Being able to purchase some kind of health restoration would have been great.
Otherwise, great game!!