Speaking as a parent of two children who we have spoken exclusively Spanish to, and who picked up English from their environment, friends, and school. There has not been any impact. And this is coming from the teachers, who are usually extremely surprised to learn that we speak only Spanish at home.

You underestimate the ability of children to absorb knowledge from their environment.

As a matter of fact, if anything, it has been a net positive. Kids at a young age have a huge curiosity about languages and having bilingual kids in the classroom encourages the other kids to learn. My first graders class begged to have my daughter teach them some Spanish, and the teacher set aside some time for her to do so. The other parents heard from their kids, and thanked the teacher for it!