You can say they are not from Mexico but they are.  Just because they were born in central America doesn't mean that Mexico isn't the problem.  They are entering Mexico to cross the border to the USA.  
So they are coming from Mexico, really no difference what nationality they are in the end, they are illegal.  What if ISIS members were using Mexico to get into the States?  Not a problem because they are not Mexicans.  I'd like to see some evidence to back up your claim more Americans are going into Mexico illegally.  This is so unbelievable that it has to be made up.  Unless you mean Mexicans returning from the USA.