Just a bit of common sense here... if you go to visit someone, and their door is ajar, vehicle running, do you just leave? Or wait to see who comes out the house to get in the vehicle that is running? As my avatar shows, I trap cats. If I am returning a cat to it's home, and the same situation was presented, I would sit in my vehicle and wait for the homeowner to get come out. Because most likely, they were getting dressed, or had to run to the bathroom, etc, but with the vehicle running, I would assume they would soon come outside to leave and thus I could let them see the cat was OK that I was returning, and then let it out of the trap.
S0000 if you were going to check on the wellfare of CHILDREN, don't you think you would wait to see if the parent and kids came out of the house? I'm beginning to wonder if the social worker even went to the house. Maybe just said they did because they were suppose to be, but it was a holiday.... maybe they had plans and didn't want yet another case delaying their plans? I shouldn't be so skeptical.