Given that there were absolutely no widespread studies at that point, they had to go on priors. And the 6 ft guidelines was based on the belief that if COVID spread mainly through droplets (which was the most likely theory at that point). The children aspect was again based on limited information available at that point.
With all the data now, we see that COVID affected older and less healthier population. They had no idea at that point, conclusively so always erred on the side of caution. All this house investigation is a Republican witch-hunt.