X-rays can't fly around in a room at will. X-rays are highly directed radiation beams. If there is radiation, there are very few areas exposed to light. So if your teeth are being imaging, your baby is not exposed to any radiation, even without a lead apron. We mainly use lead aprons to treat patients' inner peace! Advances in technology have led to a significant drop in the x - ray dose of any test. The lowest dose of dental X-ray!
The following websites have the answer of qualified medical experts, who are experts on radiation. Here's what I found out there:
"The level of X-ray scattering of x-rays from dental x-rays is too low to harm an embryo or fetus at any stage of pregnancy."
"So the typical dental exposure dose is equivalent to about half a day's inevitable natural background, which is not worrisome."