Covid era protocol
A lot depends on how long ago they were vaccinated.
Here's a chart showing in July the vaccinated that got COVID really ramped up. Most of them were vaccinated in Dec - Jan. You can't really depend on vaccination to give excellent protection after five months.
So, there is some risk for the chemo person. Risk would be less if that person had their third shot at least two weeks ago.
The kids risk level is doesn't change. Kids are continually exposed to vaccinated and the unvaccinated at home with their parents or in school. The lunch setting should not matter.
Particularly at your age (no offense) you are entitled to err on side of caution. Not so sure I'd say no masks outdoors. You should wear one.
@RTrent… the guest received a booster shot a little over two weeks ago! Thanks for the info!
bub said:
Particularly at your age (no offense) you are entitled to err on side of caution. Not so sure I'd say no masks outdoors. You should wear one.
I had planned to add my age to my initial post, but I didn’t want to be accused of bragging!
I think if you're outside with distancing between household groups you don't need masks.
I would request anyone who goes in to the house to use the bathroom put on a mask for the few minutes they'll be inside. If you can keep the inside well ventilated, then maybe dance around with a can of Lysol after your guests leave, then any risk of transmission from people going inside for brief periods of time will be mitigated.
Your biggest unknown risks are the 10-year-olds, since you don't necessarily know who they've been in contact with in the last few days. Then you have someone who is at great risk if they contract the virus. You can't force the person who is on chemo to wear an N95 or double mask the whole time. But if you can kindly encourage them to find some way to reduce their own risk you can relax a little.
I would focus on the combination of the two unvaccinated kids and the person who has a high risk profile for a COVID-19 infection.
Personally, given the current flux, i would suggest that people mask up when they're not eating, and maintain some distance. I would wear a mask myself (cheerfully) to set an example, and have masks available (by the house door?) to help people not "forget." If weather drives the event indoors, definitely ask people to mask up, leave as many doors and windows open as possible, have fans running.
This is because of the extended time period, the multiple households, the kids, the high-risk person. If meeting neighbors outdoors, uncrowded, and vaccinated, for an hour or two, i would be comfortable letting the masks go.
As an immuno-compromised person myself, even in a low-Covid region i wear disposable food-handling gloves and have a small bottle of sanitiser on the table/in my handbag if I’m eating out. I wear a mask when I’m not eating/drinking and I’m very careful about the distances I maintain from others even if I know them. (I don’t expect fellow diners to glove up; it was a tip from my immunologist & my oncologists)
I carry my own metal drinking straw, cup (it has my rice milk in it), wipes, tissues and water bottle.
Just me being extra cautious since I have so many issues with medications. I have noticed, however, that venue serving staff here continue to wear disposable gloves and their masks for table service no matter how minor the task.
No self-serve buffet; people choose and one person only handles the tools &dishes to serve up and hand direct to the diner.
Hope your occasion goes smoothly! 
Seven extended family members are coming for lunch on Monday — five of them are fully vaccinated, the two kids under 10 are not. Another guest joining us is on Chemo and at heightened risk.
I believe that, weather permitting, most of the time will be spent outdoors, and no masks should be OK. However, if it’s too hot, too wet, and, as a portable john will not be available, people will go in and out of the house.
As the host, I think I should set guidelines ahead of time. No masks needed on anyone outdoors; social distancing consciousness; and masks on the kids while indoors, or vice versa?
What would you do?