Oh, don't take me the wrong way, Nonno, I'm on your side! I'm sure it was awful.
But your DH made a one off decision, that sounds sensible to me from the way you describe it.
If someone was concerned enough to inform the police, why didn't he see them? If that was me, and I really thought the kids were abandoned, I'd have stayed by the car until an adult turned up, then probably given that adult a piece of my mind! If no adult turned up, I'd have rung 999 and got the police out immediately.
The person who reported your DH sounds more like a busybody than a concerned passer-by.
It just annoys me that those of us who agonise over the decision of leaving our children a few metres away for a couple of minutes, or feel guilty about a tap on the hand occasionally are made to feel like child abusers, when those who genuinely neglect their children don't give a shite.