Tas, First off my heart goes out to you. It's always hard to lose a loved one but especially when it is your own child. It doesn't seem fair that you out live your children but remember that as soul we are all eternal. So age of the physical body does not matter. I can't say for sure if your son had a carry over of injury from the pervious life or not. However what I do know on a soul level is that souls that don't live very long in the physical world usually do so because they chose to come back and work out mass amounts of karma within in short time period during a physical incarnation. These tend to be souls that are on a mature or old soul level of spiritual evolution so they chose a lifetime with heavy hardships or handicaps to overcome that most of us would not want to handle.
By doing this they usually effect those that care for them or those that they come into contact with and change their consciousness both mind and heart by their mere presences of being here. The phase ( before the grace of god go I) comes to mind. I have no doubt you had a very special connection with your son on a soul level as you have been moved and changed inwardly from the experience and have grown from it on a soul level by leaps and bounds. So in a way you have been part of your sons process in spiritual evolution. When you both meet again I am sure it will be on a higher dimensional plane of reality that is brighter than ten thousands suns.
Love and peace always...
P.