First, I need some sort of example of who exactly you are using as an example, illegal immigrants who've had children here, or people under visas. Right know I'm going to just explain for both.

Illegal Immigrants: It doesn't matter how long they've been here, they aren't legally immigrants, I've said this so many times. They only pay taxes to try to gain favor and get in legally, they don't have to. If a person comes into America illegally and gets deported after having a family, it is that person's fault for the splitting of the family, not the government's, as they decided to take the risk of separating their family coming here illegally. If they've come here illegally, most of the time they either because they could never come here legally, their country is in conflict, poor, in famine or a mix of all. I do think there should be better policy when it comes to countries in conflict or suffering from famine and but sadly some of the countries suffering from this in the worst way possible are inescapable or full of terrorists.

F1 + F2 Visas: They only pay a tax to be educated in the U.S. they don't all pay taxes to the American government. If these people are here to gain education, they can use this education to gain citizenship, and then move their family here.

Both: It doesn't matter how long they've been here, they aren't legally immigrants, I've said this many times.

Global Warming: Temperature increase of anything would be good for humans as we are made to survive in warmer conditions. Agriculture would be better and we would be able to grow new plants, look at countries near the equator as an example.