I am a honorably discharged US Marine trained in urban combat and I would not run it to that store in this scenario. it takes more guts to stay outside knowing your wife my be killed and protect your child it a bad situation either way in this case the one that is not "movie cool" is the better choice you odds of rushing in and saving the day are almost zero.. and more than likely will cause an escalation of the already on going violence possibly resulting in more death/injuries.
I would dialer 911 and move the car if I felt I was to close. My wife and I have already discussed these type of situations and have both agreed our child comes first in any life or death situation. I would be pissed if she came in after me and left my son alone as she would be if I left our son alone and came it to save her. When your a parent your child's safety come above all else else even your own life or that of your spouse.