I need recent information on all US households who have kids.  Among
these households that have kids, on average, how many kids are in
these households?  This would have to be the most recent statistic, ie
2005.

Census 2000 data is usually the best source for this data, but
unfortunately the Census does not provide a lot of estimates data. 
Each company that provides estimate data takes the Census baseline
data and then comes up with their own set of calculations to determine
the estimates.  As a result, the data values will differ depending on
your data source.  There are companies who go from the top down and
determine a multiplier for, say a county, and then apply that
multiplier to all census geographies in the county regardless of
population distribution or population movement throughout the county. 
And there are others, who work from the smallest level on up and there
are probably t.  I like to work with Census 2000 data whenever
possible.

This data was pulled for the Entire US

Basic Variables 2000 census
   Family households  			71,787,347 
   Population In Family Households  	231,374,718

Calculate: Pop. In Family HHlds/Family HHlds = 3.22

Basic Variables 2005 estimates 
   Average Family Size  3.22 
   Family Households  	73,804,082 
  

Census Source: www.demographicsnow.com (using www.census.gov data
maybe through a third party)
Estimates Source: www.demographicsNow.com (using Experian/Applied
Geographic Solutions estimates)