I hope the leak has been fixed. It would be good to have your kids checked by a doctor. We had a leak after the contractor incorrectly installed a new gas stove; we called it in severa times but it wasn't detected for a few years. Most of the gas risk is from fire, rather than to a person's health. There are no heavy metals or similar nasty chemicals associated with natural gas. The smell of natural gas is a small amount of tracer (similar to skunk odor) that is used to alert people that there is a leak. I am a petroleum geoscientist, not a medical doctor, but most of the online "natural gas health" info was associated with living near gas wells, not having a leak in your house (different gas compositions).