Your SIL will decide for herself when / if she sends her DC back
Same as you can
If fewer kids attend for at least the first few months, then it is easier to organise social distancing
So that actually helps others
Even when the government end lockdown, they can't bring back the previous "normal" you enjoyed
They can't actually force most people to go out again,
especially not to go out and spend on non-essentials like restaurants, nail parlours, cinemas etc
Many folk will be skint and building up savings again, or paying off debt,
even if not worried by the virus
Some businesses will not survive with the reduced customers,
especially if their clientele include a significant number of shielded / vulnerable / older people.
Holiday flights are unlikely to return this year
You'll get a lot of things back eventually, but not all