Sierra's posts have been exactly in line with my experience and training in the mental health field, and as a mandated reporter working with children.
I would disregard the advice to think about what you want to accomplish by calling. It can tear you up to try to make judgements about what actions CPS ought to take, and its really not your job and not a decision you can even be a part of. If you have concerns, then you should call CPS and leave it to them to decide if your concerns are legitimate or not.
That said, if I were in your shoes I would consider the following from your list worth reporting, but I would try my best to cite very specific examples of these behaviors along with dates:
|-he is often hit, slapped, screamed at, pulled around by his hair
This indicates physical abuse, and I think they will ask you to describe the incidents that you witnessed this and to give details, so be prepared with that information.
|-he is always ridiculed when he has an "accident"
This shows that he may be subject to emotional abuse. Add to that, some huge percentage of child abuse occurs around the issue of toilet training. I think this is important to mention.
|-they rarely use a car seat for either child in their minivan
This is an obvious legal issue. I would be prepared again, to mention specific incidents where you witnessed their failure to use a car seat.
|-sometimes they will come over to visit at 4 pm, and the 3 1/2 year old will still not have been fed ALL DAY, or will have only had bottles (up to 5 in one day) of cow's milk
-the 9 month old has fallen down the stairs at least 3 times
-3 1/2 year old is left to play outside, by himself, no supervision or even an eye on him from a window. they live on a busy street and do not have a fence.
-he doesn't like to have his hair washed in the bath tub, and so it never gets done
All of this indicates neglect. I think it is important to mention the fact that he is often dirty -- this is an indicator that tends to get the attention of CPS.
They will ask you further questions. Some of the other things on your list may come up in the course of the conversation.
Keep in mind that while CPS does not follow-up on every individual report, they are more likely to follow-up if there have been previous reports. As a mandated reporter, I have had CPS intervene in situations simply because I was the 2nd or 3rd person to file a report. Your report may well provide validation for someone else's (or vice-versa.)