If have minor child(ren), you'd better write a will to appoint

guardian. The court can appoint anybody if they think it is good for the kid. We appoint my hu*****and's brother to be my child's legal guardian in the will. The sole purpose for us to draft the will is to appoint guardian for my child. (We use QuickenWill software to do it, quite simple.) You can also appoint your parents to be the guardian even they are not citizens, if you think it is good for the kids. BTW, you should ask the permission of the person that you want to be the guardian.

You can Google "will minor guardian" and lots of info will be available, e.g.,
http://militaryfinance.umuc.edu/estate/estateplan_guardianship.html