Who runs the ASC? The school or a provider?
I would think if they are already running it, then trying to convince them to allow reception age kids has to be the best solution? Although 4.15 isn't ideal. Worth approaching them now and asking what it will take to allow reception age kids?
It sounds bonkers. Do they think that all reception age children have a SAHP who then all go out to work in Y1?
Do you know anyone already at the school? They might know what others do.
I looked for a CM for my DS before he started school and couldn't find any that said they'd do a drop/collect from our school.
But when he started school I saw there were a few childminders who dropped/collected from the school.
I recently considered using a nanny for one day a week for DD and I found a possible person through a school mum.
You are doing the right thing by thinking about this now.
Good luck, hope you sort out a workable solution.