What happens to kids when their parents get deported and they dont have anyone who lives in the USA?

Nothing really.

Explanation:

As of now or since 2015 at least if you are an illegal immigrant and you have a child It Is by law they have to give you a citizenship. This is how a lot of immigrants also get into the United States for free these are known as anchor babies. But if they have kids that come with them they're most likely getting deported with their parents. But I'm also pretty sure if they have children and no one knows about in the US then those children will most likely go into foster care here in the US if there is no one who that in the family that has illegal citizenship in the US.