Since this is the Michigan forum lets assume he is from MI.
I'm not sure if a preschool is a school under Mi law:
"750.237a
(b) “School” means a public, private, denominational, or parochial school offering developmental kindergarten, kindergarten, or any grade from 1 through 12."
but if it is:
"28.425o Premises on which carrying concealed weapon or portable device that uses electro-muscular disruption technology prohibited; ...
(a) A school or school property except that a parent or legal guardian of a student of the school is not precluded from carrying a concealed pistol while in a vehicle on school property, if he or she is dropping the student off at the school or picking up the child from the school. As used in this section, "school" and "school property" mean those terms as defined in section 237a of the Michigan penal code, 1931 PA 328, MCL 750.237a."
Michigan Legislature - Section 28.425o
Lets not start a open carry debate but it would be the only sure legal option in MI.