Good point. But, you have to think the kid will either have assimilated as he grows up and becomes (what is it) 40 years old. Either that or he will be so extreme that he can not be elected. There is a pretty good vetting process through the political parties.
Age for a US president is 35 years.
I think this point isn't a big enough deal yet. There is a concerted effort to get mooslims born in the USA. I believe that the long term effort is to get a Muslim president that will enact Sharia.
Don't discount it.