Tried working it out once 2 years ago based on percentages of Latinos in public schools, national population, border crossing trends, welfare trends, hospital statistics etc. but had to guess on how many were legal from the statistics, kids per family, single vs married parents, blah blah. Ended up spitballing it between 30-35 million by downplaying # of children per family to 2, saying 1 parent and dividing the Latino population evenly between legal/illegal. Not perfect, but probably closer than what anyone else will tell us.