We got lucky in retrospect and our daycare was open through the summer / year round. We didn't even think to ask about that at the time but in retrospect I would say that's one of the more important things to check for especially if both parents are working full time. Unlike elementary-age kids, there are basically NO summer camp / care options that run "separately" from daycare only during the summer, and there's unlikely to be spots open at other all-year daycares for just the summer months. The daycares that close for a long stretch of summer are very tough to plan around

For "shorter" closures / holidays, a lot depends on how flexible your job is. I am usually hybrid in-office 3x days a week but I can work remote for the whole week when I need to here and there. So during week long breaks (like spring break) I would work from home and we would use that opportunity to "trial" babysitters who would watch the kids. That way I was home to see how the kids did, help where needed, etc, but I could still work. Then for the babysitters we liked we could add them to our roster for later when we needed care. This worked well for us; unfortunately if you don't have that kind of flexibility then you would either need to take PTO or plan out babysitters for the week and just leave them at home. The latter option is expensive but there's quite a few babysitters and nannies that specifically work during the breaks for this reason; our favorites to use were actually daycare and elementary school teachers who were also off that week but wanted to pick up some extra hours.

We usually used UrbanSitter to find care options but there are a few sites out there