Mexico, like most countries, will abide by the internationally agreed upon security standards for liquids and gels. You can read these on various sites, if you speak Castilian / Spanish, such as the Mexico City International Airport site
here.
Los pasajeros y la seguridad en los aeropuertos: Equipaje de mano. ¿Qué puede llevarse?
Los artículos permitidos bajo estas nuevas medidas son: medicamentos en la cantidad necesaria para la duración del viaje; leche, jugo y alimentos para bebé, siempre y cuando el menor vaya a bordo de la aeronave; productos para necesidades dietéticas especiales, cilindros de oxígeno gaseoso de uso medicinal, con prescripción médica obligatoria y discos compactos, otros artículos electrónicos, computadoras portátiles, ropa y calzado.
So, you may take medication sufficient to last the entire trip (best with a prescription or of OTC doctor's letter, even better if translated into Castilian Spanish) (hint: take a prescription with the generic name of the medication in case you need to replenish in Mexico - you may even be surprised to find it is much cheaper. A friend who requires over $600 medication
monthly in the USA was able to get a six month supply for USD $160, both meds made in Scandinavia by the same pharmaceuticals company - go to a
"farmacia de primera clase", a first class pharmacy with professional pharmacists, to ask if you have to, and yes, there are other classes of pharmacy.)
Ice packs -
very probably OK, but as much in the US as in Mexico, some official may get officious. You can also request ice from the FA and the hotel, of course. If possible highlight the part of the prescription that states the medication must be kept refrigerated. Keep calm, be prepared to explain, just in case. Ah,
have a copy, and if you are taking the infant with both parents, you are OK; if only ONE birth parent, be sure you have a notarized letter authorizing you to travel to Mexico with your child - or you may find yourself with some difficulties.