Grandparents! They signed up for this when they had kids, or at least it’s common practice where I live.

WFH, summer kid camps that did free or cheap activities during the day, friends who also had kids (returning the favor another day), relatives (mine were extremely unreliable), and all else fails paid child care.

My relatives were absolutely useless for childcare. Its fine if you don’t want to look after your own grand children, just say so. But under no circumstances repeatedly say you will have the grand children then back out on the last day, many many times.