You dont need anything, they will grant ur child 3 months visa at the airport, which u can renew every 3 months at the immigration office, or u could send a copy of ur marriage certificate and get a relationship certificate between ur kid and grand mother and get a 1 year visa which can be renewed yearly.

I know its hard but but not impossible. I can undertsand what uve been going through.

Imp: Dont forget to carry lots of foods for ur baby, those liquid bottles of formula, ready to feed and diapers and plenty of nipples or bottle liners,extra clothes and ya get lots of toys, coz baby gets bored every now n then( go to dollar store). Dont rely on ticketing agent, call the airlines 24 hrs before to let them know if ur kid is less than 6 mts, they ll arrange for bassinet and other stuffs.