Radon in the home

Is anyone knowledgeable about radon in the home? I know that levels below 4 pCi/L are “acceptable”, but are they really safe when you are pregnant and/or have babies in the home?

I’m house searching and found a home I LOVE but it has a radon pump. I don’t have any info on the levels that were measured prior to the pump being installed, and I also have no info on the current radon levels. I read that a radon pump will help reduce the levels but even if it’s considered acceptable, that doesn’t mean it’s safe. I guess a level of 4 is still too high according to some sources.