I have seen recommendations that it is okay to extend your family group, to include another family group (neighbor, your sister's family, etc). But everyone in the group needs to be limited in their movements. SIL is doing that in Seattle. Her BFF has a nanny normally, so she is is self-isolating with BFF.. Nanny is watching the kids while the parents are WFH. Everyone in that group is self-isolating from the rest of the world.
The larger the group gets, the harder it gets to control, because it requires a lot of trust. With the size of a sports team or several families in a neighborhood, does not inspire trust. Too many people are going to do "just one thing they shouldn't do" and people are going to get sick because of it. Being happy sports teams can still practice is not an example of proper social distancing. Random play dates are not proper social distancing. Two working families, rotating childcare days are not playdates. So that's why you are getting blowback.
That is different than medical workers and even grocery store workers who have to go to work and put their kids with someone, too. Yes, their risk is higher because their job makes them more high risk, but I home these people are trying to stay within their chosen circles as much as they are able and not put their kids with a different person outside the circle every other day. So a group of nurses, or 3 people at the grocery store, who decide to share childcare, but are prohibiting their kids playing with the neighbor.