Kidcreate Art Studio in Old Town also allows for drop-in camps. We've used them a few times and they are great.

Same as above, we use Steve & Kates through the Bright Horizons Backup Care system for two weeks a summer. The kids complain about going because they say it's boring (it's less structured so they have control over their day and what they want to do) but always end up having a total blast. My kids are in 1st and 3rd.

There are a lot of forms, so I'd recommend signing up online first rather than just showing up because you do need to present forms, birth certificate and a bunch of other stuff. It's a lot for just one day.

My son has been going to Steve and Kate's Alexandria occasionally (on days he doesn't have a full week camp) in the past 2 years. It's less educational than some other camps, and they play video games sometimes. But he loves it and always has a blast. The staff are nice too. As you said it's only for one day so your kids will be totally fine, especially they're older. My son started going when he was a 1st grader.

I register through Bright Horizon's backup care system (as a benefit from my employer) so I've no idea if you can just show up the day you need coverage. I always register at least a day ahead.

I need one day of coverage one week this summer, and google is pointing to me to Steve and Kate's - I've heard of this camp before but we've never attended. It seems like you just show up on the day you need coverage -- is that right? (Hard to imagine based on registration processes for other camps!). Any recent experience/what is it like? My kids will be rising 4th and 6th. It's only for one day, so I figure they'll be fine, but any info would be appreciated...