I'd say, if you have a family who are likely to want to push for more than you want to do, that it might be best to keep it strictly professional and avoid any discussion of 'difficulties'. You are running a business and can state your on working hours.
But I'd keep it clear from the outset- not 'I will take more holidays' but 'I will be closed the weeks of xyz'- that way there is no discussion and it is clear that they need to find alternative care for those weeks- you can refer them to your LA list of providers, childcare.co.uk and maybe any local holiday clubs etc.
I'd send a letter to all families stating something like 'due to changing needs of my own family I am adjusting my opening hours (or adjusting the weeks I take as holiday) to xx weeks closed per year/closed the weeks of xxx. As this is a contractual change I am obliged to give 4 weeks notice but as this change will require you to make alternative childcare plans for those weeks I am giving you plenty of notice so you can do that with less urgency (insert links to LA CMer list etc). Please sign below to agree these contractual changes (2 copies) and keep this notice with your copy of our original contract.'