When to tell HMRC re childcare

[Iloveapplepie]

So dd starts school second week of September. She is in childcare until then. Once she's started school then, am I right in thinking I have a month to confirm a change?

You do have 30 days yes however if you do delay it for the 30 days you will have 30 days of an overpayment to repay.

I'd also tell them now. Having to repay a lot, even when you have told them about a change in circumstance, is not fun (bitter voice of experience).