So, we will have the kid stand in the middle of the carrousel.
The magnetic hyperfine field has contributions of: the spin dipole, the orbital contribution and that the electrons are INSIDE the nucleus. So, we have the electrically charged ball on the edge or maybe even outside the carrousel whilst we spin around (equivalent of a moving charge). The child in the middle sees a change in magnetic field on its magnetometer.
Also, the bar magnet i hold shows a magnetic field.