no no, I mean audio record them. you'll amaze how they change on the way that they speak and their tone. My elder girl is now 3.5 yrs. but she use the baby tone to speak adult sentences, very funny. So, the 1st "pa pa" or "ma ma" will never come back again
On top of this, if the 2nd one is not too further apart from the 1st one, you can better recycle your elder son's resources as well, e.g. toys, school related items, clothings, etc.
My younger son is 1.5yrs. younger than my daughter