From what I have read, if you had 2 kids listed on your 2007 return you would get the extra $300 a piece for them in the check in May/June (as the “refund” is estimated from the 2007 return). If you then have another kid in 2008 which would then cause you to have 3 listed on your 2008 return you will get the extra $300 credit at that point (as technically it is a credit of sorts for 2008 taxes).