Firstly, the first query does not include any aggregation so doesn't need a
GROUP BY clause:

SELECT
ClientsByInsuranceAndServiceDate2.Name,
Person.BirthDateTime,
Person.CreateDateTime,
ClntsInsSvcDatesByAgegroup.Expr1,
Person.LastName,
Person.FirstName,
Person.MiddleInitial,
Person.PersonID,
IIf([CreateDateTime]>=[Forms]![FromToDates]![Text0] And
[CreateDateTime]<=[Forms]![FromToDates]![Text2],"N","S") AS Source
FROM (Person INNER JOIN ClientsByInsuranceAndServiceDate2
ON Person.PersonID = ClientsByInsuranceAndServiceDate2.PersonID)
INNER JOIN ClntsInsSvcDatesByAgegroup
ON Person.PersonID = ClntsInsSvcDatesByAgegroup.PersonID
WHERE Person.CreateDateTime BETWEEN #2/1/2007# And #2/28/2007#
ORDER BY Person.BirthDateTime, Person.CreateDateTime, Person.LastName,
Person.FirstName, Person.MiddleInitial;

You seem to be mixing parameters (the references to the controls on the form
in the IIf function call) and date literals (in the WHERE clause) here.  Is
this the same date range in each case?  If so then the IIf function call will
always return "N".  If they both represent the same range then use the same
parameters in the WHERE clause too.

As regards the second query:

SELECT
COUNT(*) AS Kids,
EnrolliesQuery.Source,
[Source]=IsNull("") AS IFF
FROM EnrolliesQuery
WHERE Expr1 ="K"
GROUP BY Source, [Source]=IsNull("");

I don't see the purpose of the expression [Source]=IsNull("") AS IFF.  
IsNull("") will always return FALSE, so Source = FALSE is also going to
evaluate to FALSE as Source is a string expression.  If the date literals and
parameters in the first query do represent the same range and I'm
consequently right about the expression in the first query always returning
Source as "N" you can simply include it as a constant in the second query's
SELECT clause if you really need it retuned as a column:

SELECT "N" AS Source,
COUNT(*) AS Kids
FROM EnrolliesQuery
WHERE Expr1 ="K";

Ken Sheridan
Stafford, England