LINQ child records null

I used Entity Framework to create my database schema and generate my code. I have a table called Employee that has child records in a DaysOff table. DaysOff has a foreign key to Employee and there is a 1 to * association in my model. I ran a LINQ query on the Employee table and expected that my Domain.Employee object would be populated with the DaysOff but the DaysOff are null. When I drill down in the Object I see "employee.DaysOff.Count threw an exception of type System.ObjectDisposedException". Am I wrong to think that the child records will be populated? How would I do this? Here is the method I call to get my Employee:

public static Domain.Employee SelectEmployee(int employeeId)
{
    using (var db = new EmployeeEntities())
    {

        Domain.Employee emp = (from e in db.Employees
                       where e.EmployeeId == employeeId
                       select e
                             ).FirstOrDefault();

        return emp;
    }
}

EDIT: A combination of the accepted answer below and the comments (all up-voted) helped me to solve this (yay!):

public static Domain.Employee SelectEmployee(int employeeId)
{
    using (var db = new EmployeeEntities())
    {

        Domain.Employee emp = (from e in db.Employees.Include("DaysOff")
                       where e.EmployeeId == employeeId
                       select e).FirstOrDefault();

        return emp;
    }
}