We did this.
You need parents to take only some leave together (main family holiday) and then have separate times with Dad+kids and Mum+kids
Holiday clubs (I was always booking for the next one as soon as each hol finished)
Investigate every possibility for flexible working: see if you can 'bank' hours and take some TOIL, or ask to compress hours during some of the hols to give extra days. Once DC are age 10+ (ish) it becomes possible to WFH without undue distraction.
Au pair for the summer if you have room (only with older DC though, they're not qualified and shouldn't have sole charge of very small DC)
Make friends with your DC's friends' parents, and see if you can arrange some child swops#
But at the end of the day, just like everyone else, you'll almost certainly end up paying for quite a lot of it.
Remember that childcare is a joint expense, for it allows both of you to work. So you need to look at how much the household income rises, as well as how much household bills increase.
Factor in also things like job security - two earners is more resilient than one, being in the workplace means greater changes for progression and promotion. Also the longer term view - even if you see no increase in household disposable income, what would be the situation in 10 years (rather than 5) when you don't need as much holiday care - if you've been working, then disposable income increases considerable (costs go down) but if you haven't it doesn't, and you are perhaps then faced with job hunting after a protracted break. Also cost to you in old age if you have fewer years in your pension