...you DO NOT build trust in a dog you've only had for one day AND which immediatey displays an aggressive behavior! The child and the dog should have been completely isolated. This isn't rocket science.

"...these parents are college grad, well educated, church going, extremely nice and smart people." Those are all nice things to say and likely true, but they definitely lost the sense of "good judgement" (you left that one out) concerning the well-being of their child. The flags appear as obvious.