When you combine two or more tables, variables that are "." (not applicable) on any of the variables will be excluded. The KR file, which I believe you are using, includes all children born in the past five years, whether they are alive or not. That is probably the 11,040 you are talking about (I don't have time to check that). The questions on ARI, etc., are limited to children who are alive. Some questions in the KR file are limited further to children who are alive and living with the mother, or limited to the youngest living child. Children for whom the question does not apply are coded ".". That's why you are getting different n's. That has nothing to do with svy. You could repeat without svy and you would see the same thing.