Must we offer benefits to our summer help?

Q: “We have summer full-time temporary help (high school students). They are paid $10.00 per hour plus time and one half for any hours worked over 40 hours. Because they are considered full-time temporary employees, must we offer them medical, dental or flex spending benefits? We offer other full-time employees these benefits from day one. We consistently have not given benefits to full-time temporary help.” – Dorothy, Michigan