For the "Torque on a merry go round," for the first part: the total torque(t)=the sum of all of the moments of inertia * the angular acceleration.

Find the acceleration  by dividing your angular velocity ( remember to change to rad/s) by your time.

Then just add up the moments of inertia: for each child it's mr^2, but since the merry go round is a solid cylinder, it's moment of inertia is .5mr^2.

 Hope that helps