A note about story changes - in my trial advocacy class, I was taught that people who are being truthful will have small changes in their recounting of events, because you're going through the process of recollecting it in your mind and recounting what you remember. There are tons of little variables that will effect the amount of info you pull - things like how the question is phrased, how tired the person is, etc. Two people who saw the same thing or experienced something together will tell things a bit differently, or even disagree and contradict each other.
When a story is exactly the same, time after time, with no variability, that's when someone is more likely to be lying because that points to a rehearsed story. You're parroting back what you memorized. When you have two people telling the same story, with no variability between each other, or from recounting to recounting, that's when you definitely have to question their stories.
So, I'm still on the fence about the parents. I've not seen a glaring inconsistency - just little variability. JMHO.