freaking out here

We had a radon test done in our home because we are selling. It came back at an 8, the recommended limit is 4 according to our realtor. I am now freaking out that our 6 month old and 4 year old have been living in this house. We've lived here two years. Anyone know anything about Radon gas? Am I overreacting? Anyone have any experience with this?  We are having a mitigation system installed next week 😔