If a parent wanted their 7-year-old to walk home from school alone and were happy to take full responsibility for the outcome of that decision, why would the school pass it on to another agency? There would be nothing to report, surely?
Because the school do have a duty of care to report safeguarding concerns - even when parents believe they are right.
If the school thinks that a particular child will be put at risk by walking home alone, it is not the schools place to "not allow it" as you said upthread. Spending time trying to persuade the parent otherwise is not the role of the school. It is the schools place to report their concern to the Ch Serv dept, and if they believe there is an immediate risk of serious harm to the DC, to call the police.
As for examples I've seen - and my role has exposed me to failing, rather than average schools, so this is by no means representative - I've seen headteachers collect and drop off parents to appointments with probation to ensure the parent isn't in breach (which in turn would lead to the DC being placed in care), I've seen FLOs agree to provide childcare on school site late into the evening while Soc Services try and secure an emergency court order, routine feeding, washing and even dressing of DCs on arrival at school (uniform in a bag left with the pajama'd child every morning by the parent who wasn't able to help the child dress) - oh, and let's not forget the minibus affectionately known as the "child catcher" which collects all the pupils with poor attendance from home every morning ( this one was eventually legitimised by using Pupil Premium funding to pay for it). One HT I knew (admittedly a few years ago now) even established a nursery/crèche facility on school site, using school facilities and staff, but in her own name as the sole company Director - and offered free places to families she thought needed it at school expense. That was an interesting mess to explain to the (very naive) Governing Body, who were ultimately responsible!
I'm not saying it's easy - schools are picking up the slack from other agencies who are squeezed due to funding cuts and as the school actually works with the DCs they know the difference these things make to the DCs lives and are doing it for the good of the DCs who they know and work with.
But, many schools I have worked with do stray a long way over the boundaries of their role in order to make the DCs lives easier/safer/better. A HT shouldn't expect to spend 2-3 hours every morning with a queue of parents at their door, all seeking emotional support for the most recent drama in their lives.
In the case of walking home alone, it is sufficient to acknowledge the parents request, and refer on to the relevant partner agency if there is concern about the child's safety based on the DCs age, maturity or any SEN that may be relevant.