Why isn't it? Even I think it was okay and I think everything most parents due is wrong.
Because he didn't commit a crime. There's a difference between actually commiting a crime and 'technically' commiting a crime. Opening a Christmas present early isn't a crime, at all, period. If the mother wanted to get the police involved to scare him that's one thing but he was charged with a crime. That's ridiculous.

I also think she should have waited for him to do something that actually resembled a crime in some way before she called the police, but that's just me.

Edit: Normally I think these kinds of things are funny, but for some reason or another I don't in this case. Not because I disagree with what happened, but it just genuinely didn't laugh. Dunno why.