Ronaldo. I am in agreement that DC's need a main CARER to see to their needs. I am NOT in agreement with you that it NEEDS to be the Mother, and I am NOT in agreement that it needs to be until they are 5yo.
Most Lone Parents are not Lone Parents through choice. Most people who have DC's with multiple partners don't do that with neglectful intentions.
I personally have 4 DC's, with 3 different fathers. With DD's father, we weren't married, but were engaged. However, I lived with my Granny, and when I found out I was pregnant, I was kicked out, and due to housing rules, had to move 600 miles away to an area that I had a 'local connection' to, in order to gain secure housing for me and my baby.
15 years ago, continuing a long distance relationship, without the Internet or mobile phones, proved impossible for a 16 & 17yo.
4 years down the line, I was married, and had a baby with my husband. When DS1 was 9mo, I caught him in bed with an OW. Strangely enough, I divorced him. Why should I stay with someone who couldn't be faithful to me?
I then met a new partner, who I had DS2 with, and then DS3 seven years later. He walked out when DS3 was 4mo. After a 9 year relationship. Did I choose that? No. I expected us to continue to be a family.
So yes, I qualify as 'chaotic'. Doesn't mean I don't teach my DC's what they need to know. And if it was environmental as in my 'chaotic' life had caused these delays, then surely DS1 would have been similarly affected?
Instead he is more than likely heading to a superselective Grammar school that consistently tops the league tables for the whole country. So I scoff at those who say that a 'chaotic' home life causes developmental delay.
IMO, neglectful parenting can cause delays, but having a 'chaotic home life' is different from being neglectful. You can easily have one without the other.
And neglectful parenting certainly isn't unique to the 'lower' social class. In fact, at my Primary, with an intake that is mostly MC, with a smattering of 'council estate' (