bold by me
I work with children too, and am also a mother, and I would be very concerned if a child put their arms up for protection like that when I asked them about something. That's a very scared child. What could they be doing that's so bad they would cry when caught? Is this in a school?
O/T I usually work with kindergartners, they are usually just learning the rules, and sometimes it's just a matter of them disappointing an adult by getting a time out for hitting another child, getting a time out for scribbling on another child's homework, etc to make them upset and ashamed. They often don't like to disappoint adults by breaking the rules. If these were older kids, I would think it suspicious, but they are still young and my kindergartners cry more easily than the older kids, which is why I have to be extra gentle with them

They are usually sensitive, and don't want to disappoint adults, not to mention many are still adjusting socially. So I see tears more often than one might think.
With the older kids, the only time I see them cry and act defiant like this is if they get into a fistfight/squabble and they KNOW it is against the rules. Then usually they cry from anger and don't like to look at you when you are discussing what went wrong.
Like I said, those are just my PERSONAL speculative opinions, and reading into someone's body language is certainly NO form of evidence, in any way. I'm certainly no expert, it was just a guy reaction.
I feel the same way that you do, in that we must entertain many points of view on this thread, and not everyone will feel the same way about the case.