My husband was born in Luton, Bedfordshire. Because my son was born in the US, he is an American citizen unless there is something I am missing?

I have plenty of time until we apply for my ILR but the sooner we get things cleared up the better. My husband is a BC and I am American and our son was also born in the US. I and our son (born 2008) are here on a 3 year visa that runs out in Nov 2013. We also have a daughter born here in the UK and...