If you want to see the impact that immigration has on the United States, you can consider it from many different angles. Immigrants create jobs. They boost the economy. They contribute to society in terms of art, culture and religion. They really make the United States what it is today.
One key thing that they do, though, is contribute massively to the population of young children in the U.S. For instance, did you know that about 25% of kids who are 7 years old and younger are the children of immigrants? They may be U.S. citizens themselves, having been born here, but their parents immigrated from another country. As the first generation to be born in the U.S., they find themselves in a unique position.