You're completely wrong. The anti immigrant sentiment is mostly about low skilled work being undervalued because the application pool is filled with immigrants who usually have no other choice because of language barriers or lack of recognition of foreign education. You can definitively argue that this hurts the bottom American families the most. Those who fell to the bottom because they lost their job permanently (e.g. coal workers) don't have a low skilled job as a fall back because salaries are being driven down by immigrants. Again as I have said the downsides of immigration are an oversupply of workers in specific industries which drive salaries down. If migrant children were truly "taking all the good jobs" then those good jobs would cease to be good jobs and become low income as well. This is obviously not happening. Once an immigrant is no longer under H1B visa restrictions by obtaining a green card their salary shoots up because they can find better employers.

Finally does it matter if it is a disaster for American families especially if the newcomers will become one of those American families as well? If you want to reduce suffering in this world then you would start with those that suffer the most. Lets use refugees after WW2 as an example. As you may know Germany was divided into two pieces. What you may not know is that the third piece was given to Poland and Poland had to give Russia land on its eastern border. This means millions of polish people were forced to immigrate. Then there were the Germans of which 8 million had to migrate out of Poland. What are you going to do with such a huge influx of refugees? Just let them rot in a foreign country? Let them into your country even you can't feed or house everyone because of the war? Of course you let them in. It's the only right thing to do.