We would put the child on the carousel and call it an electron. They would hold a bar magnet, simulating the orbital contribution to the hyperfine field. They would also hold the electrically charged ball, so they would create a current while going around on the carousel. This would create the spin-dipole contribution. The fermi-contact contribution would be hard to emulate, since for that we need a different amount of spin up and spin down particles at the center. If you then use the magnetometer while standing in the centre of the carousel. You would get some information of the hyperfine contributions by the electron cloud which is felt by the nucleus.