Sorry to hear about your loss. You may need to consult a US embassy or nearest consulate in Mexico for assistance. Contact American Citizens services unit. You may also need help of an attorney. As a general rule, you can't simply take non-US citizen children to live with you to USA. Chilrden have to be adopted or in your legal custody or guardianship before you can apply for appropriate visas. A US citizen child can go to USA at any time, provided that you are her legal guardian.

If your daughter was a US citizen, her children could be US citizens as well, even if born in Mexico.

If you’d like to schedule a telephone or email legal consultation, need legal advice or help, please let me know and I’d be glad to help you. I am an immigration attorney and offer confidential consultations and legal help in matters of the U.S.A. federal immigration law to clients from all 50 States and internationally. Please email your inquiries at Attorney @law-visa-usa.com and I’ll send you a Questionnaire. Office Telephone line is 1-402-210-2040 (please EMAIL first to schedule a consultation appointment with an attorney).

Note: The above response is provided for legal information purposes only and should not be considered a legal advice; it doesn’t create an attorney-client relationship. For more information or to schedule a consultation, please visit http://www.law-visa-usa.com/contact_us.html

If you have established guardianship or conservatorship over the grandchild that is a USC, then you can bring that child here.

In order to bring the other children, you will need to establish, in Mexico, and in the US, a legal right. Where is the father of the children? You may want to explore the possiblity of adopting the children, if you are a USC. The children may have LPR or USC status through their parents.

You will have two avenues to resolve, one through the family courts, and one through the consulate and USCIS.

Because of the complexity of your situation, you are going to need an attorney.