That'swhat your constitution says - that if the child is born in the country, then that is the child's nationality.
It's always been like that.
That said, there are very few pregnant women who are in a country for a short period of time and they give birth during that time, but it does happen. So I'm not quite sure why you chose that.
The more usual one is that you have migrants coming here, either to work legally or to work here illegally. It's their children that are not at fault for the choices of their parents.
Also, American schools accept these children, and if it's going to be a problem later on, then the schools need to decline then.
It's unfair on letting the children be educated in the States for 18 years, and they know no other culture, and then tell them to go to Mexico.