Can it be viewed as a negative for PhD applications in the US if I have children?
I doubt that you will find any general problem in the US, though it is possible that some individual professors might take issue. Some labs, for example, expect long continuous hours at the bench. 

I don't know of laws in the US governing this, but there may be some. 

There are tons of grad students with children. I had two kids in the final years of my doctoral study. But, you don't say if you are a single parent. In such a case, I don't think you would find discrimination, but I do think you would find it hard. But then pretty much anything and everything is hard for single parents. 

In many subjects, of course, you can actually work while tending a child. Mathematics, for example, or Literature. Even CS folk can do quite a lot at home on a laptop. 

And note that there is nothing special about academia with respect to "giving your all". Many employers expect exactly that. 

My suggestion is that you don't mention it in applications, but because there is no need. 



And, of course, professors may have kids and are still able to work effectively.