Sleeps With Butterflies, Freudian Slit: I used the expression “sneaking” in the thread title because I had a longer expression before but then part of the thread title was being cut off and so I had to shorten my sentence somehow. Also it gives the whole adventure more cloak and dagger feel and makes it sound more exciting. As Snarky_Kong realized to his disappointment. I couldn’t really say “break in” since the door was open.
StGermain: the children never looked underfed to me. I don’t think food is the problem in that household.
clairobscur: I see that you would have gone in also. But then you (like I to a certain extent) might have the European point of view. It seems that most people in the US are thinking differently.
lobotomyboy63: I grew up in Europe (even though I was born in the USA) and the dictionary I had at home was British which is why I got into the habit of spelling some words in the British way. Even though I live in the US now. I’ll have to check with my local police department if they want calls to the ordinary number. I remember reading the same thing in the novel “Confess, Fletch” by Gregory McDonald, staring investigative reporter Fletch - Fletch finds a dead body in his vacation exchange home and calls the regular police number instead of 911, which makes the police suspicious of him - wouldn’t someone usually call 911 when they find a dead body? Fletch says “why the hurry? he’s already dead.”
Acid Lamp - not a bad idea, ask the 911 person if it’s OK for me to go into the house. But I’m sure she would have said no.
Diogenes the Cynic and John Carter of Mars are the two votes for going in. But so far the vast majority say “don’t go in”. Diogenes - are you an act first and damn the consequences kind of guy? 
Wile E made an astute comment (similar to what elbows and Lobelia Overhill suggested) - why didn’t we at least ring the doorbell or knock on the open front door? I feel stupid now for not thinking of it. Trying to think back to my state of mind that night, I guess I would say that I wasn’t sure that there really was an older sister in the house. The neighbours suggested the idea since they had seen an older girl around during the day, and it seemed very unlikely to me that the mother would have left a 6 and 4-year-old at home by themselves, but the mother does have a history (see the OP). When I asked Jill “is your sister here?” she said yes, when I asked if the sister was older she said yes, but then she was saying yes to almost everything I asked and she looked a little scared of me (I haven’t spoken to her much before.) I was figuring that maybe she was just saying yes to every question. I did send her in the house to get her sister and while we were talking she went inside several times and came out without anybody being with her. It seemed to me very odd that the sister could’ve been asleep the whole time - Johnny woke me twice by his crying (2:00 and 2:10) and my house is not right next door, it’s one over.
I wouldn’t go around the house knocking on windows. For one thing, their house (like mine) is two stories and the bedrooms are probably upstairs. Secondly, I would go in the open front door sooner that I would go into someone’s back yard. Getting in the back yard at night would seem to the occupant to be more of a suspicious activity than walking in the front door, I would think.
lieu, the new neighbour wife expressed no desire to go into the other house. Especially since I seemed to know the kids more than she did. She was the one who was most keen on calling the police.
Thalion, thanks for the law enforcement point of view. I’m in the greater Los Angeles area but in a suburban town so maybe the police have more time than I think. About a month ago my wife called the police about some kids in the park (another story) and they showed up in less than 10 minutes.
Gorsnak: I don’t get it. Something to do with having sex with the mother?
Freudian Slit: the children getting out is one thing. The older sister not hearing the child crying loudly in the street is another. Like I said, there is one house between my house and Jill and Johnny’s house and Johnny woke me up - twice!