To insist my 12-yr old collects nine-yr old from school

[Bigroundpear]

My nine-year-old is in year 5 at a small inner-city state primary a five minute walk from home. School policy is for children to only be able to walk home alone from year 6 which I fully accept (though I don't particularly agree with it).

Last week I let the school know that my 12-year old (who is in secondary school and travelled alone from year 5 for 40 mins each way - different school) would be collecting nine-year-old from school today. School emailed back to refuse because their policy is siblings who collect must be over 14.

I emailed back to say I will be exercising my parental responsibility, that it's up to me what happens to my child outside of school and I will not be there to collect, but my oldest child will. My kids have done this same journey alone together often (school is next to a supermarket they visit together frequently), I have risk-assessed this and feel confident that though of course there are risks, everything that needs to be is in place to prevent them coming to harm. I have prepared both kids for all eventualities with the school today, including that they may call social services (not bothered about this, know SS won't do anything).

I think the school is over stepping the mark, and should release my nine-year-old, however I'm sad I have put office staff in this position.

AIBU?

Send the 12 year old - If in secondary uniform they probably won’t mind and tell her if asked to say she’s 14

I used to catch 1 to 2 buses from when I was in year 6. I remember telling mum I wanted to make my own way home after school, and after football training etc.
my school was in Clapham Junction, and I lived in Streatham Hill at the time.
Journey was around 45 minutes by bus (319 and 255).
my mum used to be a teacher in her day. I am sure she made an informed decision whether to let me travel alone.
I would do the same with my daughters if and when necessary.
if I feel they could make their own journey, then yes I would consider it. Especially if we can’t pick them up.