It is a pet peeve of mine that DCF investigators think they can talk to children at school and that schools let them.
It has been a major debate in several federal appeals courts, amongst attorney members of the National Association of Counsel for Children, on the American Bar Association Child / Parent Attorneys email discussion list, amongst members of the National Association of CPS Defenses Attorneys and even at the U.S. Supreme Court.
Unfortunately it remains an open question. But I lean toward the proposition that schools should not permit DCF personnel, police or other employees of outside agencies to interview children, who are not in the custody of the interviewing person, at school.
My answer to the question "is it legal?"on avvo.com, which lays out some of my reasoning, can be found here: http://www.avvo.com/legal-answers/my-child-is-being-questioned-at-school-by-dcf.
If your school committee has a policy about visitors or interviews and you know or suspect that your child might be a target for an interview, consider adapting the form letters in my previous post to your situation.
And consult with an attorney who is familiar with DCF policies and practices.