When I’ve complained on here before about lack of childcare, the responses are all “just hire a teenager down the street to babysit.” I agree with you OP that most parents aren’t going to allow that. Just wanted to point out how dismissive people can be about how very hard it is to secure reliable childcare right now.

Dual income parents that need to juggle their work with caring for young kids are just that desperate. They recognize that there are risks, they are just willing to take on that additional risk. It's that simple.

As for us, I did screen for covid-compatibility. When I called back an old babysitter, she asked questions about what level of precautions we had been taking for covid, and I asked the same, as she lived in a household with three generations that all had at least one essential worker going outside to work. We shared info and determined we would be willing to take on that risk. But this all starts with the parent reaching out to the sitter if they are available for babysitting.

My daughter loves going to Bureau of Land Management protests!

OP, if social distancing is so essential for your family, why on earth are you attending any large gatherings like BLM protests? Frankly, your daughters are far less safe from COVID-19 at a protest than they would be at a steady babysitting job.

But to answer your question, your daughters simply say, “I’m not babysitting right now. Thank you for asking me. If my situation changes I will let you know.”

I suggest they don’t mention attending protests. If they are mentioning going to large public gatherings but not babysitting because THAT isn’t safe, it’s no wonder parents don’t understand their reasoning.