We understand from your post that your sister needs to issue a document that would authorize your parents to take care of her children for a limited period of time.
Your sister shall choose one of the following forms:
1. A Non-Durable Power of Attorney for Physical and Health Care of Minor Child is valid for the time period that she specifies in it, or until it is revoked by your sister.
Among the powers discussed in a Non Durable Power of Attorney for health care of minor child are:
to decide what kind of health care is needed, what kind of medical treatment or hospitalization to choose, to withhold or withdraw any type of medical treatment or procedure, to make any necessary effort to prolong the child’s life in the absence of a parent, to have access to the child’s medical records.
You are not giving your agent the power or authority to authorize the termination of life-support, food or hydration systems.
2. Limited Non-durable Power of Attorney for Child Care. This document is broader than the first one, and it is probably a better choice for your sister.
This type of Power of Attorney will authorize the grandparents of your sister's kids to perform all legal acts that she could have done herself as a parent.
A Child Care Power of Attorney authorizes the Agent to have temporary custody of an unmarried minor child with whom the minor child may reside and to make medical decisions in regards to said child. Parents may travel without their children but want someone else to care for the children and to consent to medical care in the event of an emergency.
By using this type of the Power of Attorney you can grant one or more of the following powers:
to authorize all necessary medical treatment, including surgery and hospitalization;
to provide for the safety of the child; his education and welfare (including placement to school and day care);
enrollment in sport activities;
signing documents in connection with the care and medical treatment;
to perform any parental acts in regards to discipline and supervision, arbitration of disputes, to act as a guardian for the custody;
other powers regarding your child (for example: travel arrangements, to pick the child up from school, etc). There is plenty of blank space in there so you can write specific powers you want to grant.
Please note that Legal Helpmate is not a law firm and we do not give a legal advice.