Not to make this a Mexican/American thing, but isn't a plane considered as part of the country in which it is based? (sort of akin to an embassy/consulate?).
Aircraft and ships are sovereign territory of the country in which they are registered. The interior of the aircraft is "Mexican soil". The mother and child are Mexican citizens. A U.S. citizen mother would have a U.S. citizen child, but it would not be considered "native born" and would not be eligible to run for President.
No. It's a fairly common myth that sailing ships are in essence floating native soil as well, and while it's slightly more complicated, it's likewise not true.