Which is best way to minimize your child's exposure to radiation?

Avoid midday sun. The biggest radiation source is the midday sun. When the sun is at it's highest intensity, it's a good time to cover up, go inside, find shade, etc. Also, imaging can cause notable radiation exposure. Not so much from xrays but from ct scans. Especially for those with small children, be judicious with head ct scans. If they bump their heads, observation for 6 hours is just as effective.