You may be able to sue them for the cost to repair  your car, if the way they were parked was not just illegal but also unreasonably dangerous (such as due to how it blocked off the alley or your garage, or blocked sight lines) and you can show that was due to that unreasonably dangerous condition that you had the accident. You can only recover the cost to repair your car, plus other out-of-pocket costs directly caused by the accident (e.g. towing cost, if any, if your car had to be towed to the shop; an emergency room co-pay, if you or your child had be checked out to make sure you were ok; etc.). You cannot recover for your stress or emotional upset--the law does not provide compensation for that in cases like this.