If singing Christmas carols and handing out candy canes to children of incarcerated moms is "in prison," yes, I do it every year with a group from my workplace. The mothers participated via skype last year for the first time. The logistics of actually getting into any prison makes volunteering virtually impossible. It is a lot of extra work for prison officials to screen, train, supervise and provide protection for ordinary civilians who come and do what? For example, one doesn't just hangout and shoot the breeze with inmates on Riker's Island here in NY. So far as cleaning, tutoring, counseling, they have a paid professional staff for those necessities. The very real danger exists of inmates assaulting volunteers or of arranging with their outside contacts to harm or use them. I don't know where you live, but you might make inquiry with the prison authorities in your area. Keep us posted. Our Lord says we minister to Him when we visit those in prison.