Child care costs - PT mum

[LJD2]

Hi, I wondered if anyone could tell me how they deal with covering childcare costs over school holidays. My ex currently has our 2 children 1 or 2 nights a week and pays maintenance. He wants to start having them half the time when he moves so said he will pay half their costs instead of maintenance.
'My youngest will start school next Sept so will have 2 in after school/holiday clubs. I work 3 days per week so will essentially be provideding childcare on 2 days per week in the hols. I might also be able to juggle my hours to avoid afterschool club. Anyone else in a similar situation? I obviously earn half what my XP does as I work half the time to look after the children, so should I pay less towards hol cover as I'm already covering the cost of having them on my days off? Any advice gratefully received!