The pandemic probably makes you think more about caring for your children. See Planning for a family emergency.
If my children are living with someone like my mother temporarily, does she have to become their legal guardian?
No. If your children are living with someone else temporarily, you can share the power to make medical and educational decisions for your child with that person.
The law calls the person who is looking after your child a “caregiver”. The caregiver does not have to become a legal guardian. No one has to go to court. Nothing has to be filed in court.
If you want your child’s caregiver to be able to give permission for medical and educational services for your child, you have to fill out and sign a Caregiver education and health care authorization affidavit. The form is also called a "Caregiver Authorization Affidavit". The form says you are sharing this power with the caregiver. It also says you swear that everything in the form is true.
Who can be a "caregiver"?
A caregiver can be any adult your child lives with. The adult does not not need to be a relative.
If you need to authorize one or more caregivers because you are afraid that immigration enforcement may separate your family from your child, use a different form. See Planning for a Family Emergency - Caregiver Authorization Affidavit.
How can I learn more about this form?
The Probate and Family Court has written some easy to understand instructions.