We can help you resolve this with an ex-partner for the sake of the children.
We think you should:
Agree how to care for kids now that school is cancelled but when work is not, including who does a quarantine with the kids if one is needed for a child who is sick.
Agree how to share extra expenses of illness and care for sick kids if a child gets sicker than the usual plan provides for and be sure the plan provides for sick childcare by a parent because childcare centers may also close.
Agree how to discuss this with kids so they do not become overly alarmed, including explaining quarantine is only temporary.
Teach children to cover their mouth when sneezing and coughing. Teach them not to put hands and things in their nose and mouth where it is age appropriate. When they are too young for that, limit what they can touch and what they play with to things you can wipe down with an alcohol wipe and keep their toys clean.
Realize that if pandemic takes the child parenting time from one parent, as when the other parent and child quarantine together, family court is a court of equity and there will be compensatory parenting time in some way whenever possible at some time in the future is it is requested. If you cooperate now it is easier and less expensive than having a court fix it later.
We can help you put these agreements into a stipulation document so it can become a binding order. It will be more enforceable then and now if we do that but more significantly, a clear boundary makes a better neighbor.