Yes carefully screen. There are dangers in mri. 1st the patient must be screened for contraindications including but not limited to: pacemaker, recent surgery of any type, cochlear implant, certain heart valves, certain brain implants including aneurysm clips, orbital metal... There are other precautions including no ferromagnetic metal in or near the mri. Otherwise, very dangerous. There is no ionizing radiation.
Probably not. Mri uses high field magnetic energy. There is no evidence that this type of energy has any negative effects on the human body. Most medical professionals agree that MRI is safe. Contrast material used during MRI scans has a very low risk of allergic reaction and can be harmful if the kidney function is impaired. Metallic implants can also have risks if that is applicable in your son's case.