Is there a reason my 3 kids age 1, 4, & 8 all have a mild fever? is there a virus in the midwest currently?

Close proximity: Fevers are usually caused by infections, and most infections are transmitted either by respiratory or hand contact, so those in close proximity, like siblings are most likely to transmit infections to each other. Young children have lower immune systems, so that may be why you are not sick too.

Likely: If all 3 have a fever, it is likely they were exposed to someone sick. Continue to watch for other symptoms. All the best.