Im sorta heading that way in my thinking too NancyA..
Girl outside car beaten(beaten to force family to do something?)(also may be why front passenger seat was empty,girl was sat there),family inside car with doors locked(terrified),perps not getting what they want so they lose it,hit child again(prob with gun butt or similar),girl drops unconcious perps spray car with bullets?,cyclist turns up,perps still angry so shoot him?