According to the Gemara Megila 15b Haman had 208 children. Why did they only hang 10 of them?
The gemara you cite would be considered aggadah. There is an accepted tradition to not accept such statements as literally, especially if they contradict mikra. According to this school of thought, he did not have 208 children. That same gemara also says he had 30, 70, 208 or 214 children. There is clearly something going on here non literal. The Rambam would urge us to consider the possible reason for such numbers and what they might mean.
Taking aggadah literally causes all sorts of problems. The list of luminaries that don't take aggadah and midrash literally is endless.