Your son will be given a printed list of restrictions. I had 100mCi Iodine-131. Restrictions were:
For 12 days: Avoid close contact with people. Journey via public transport not to exceed 1 hour. Sit in back of car diagonally from driver. Keep a separate set of crockery & cutlery & wash separately from other utensils. Don't prepare food for others or go to dentist, hairdresser, pubs, clubs or cinema. Drink plenty of fluids & shower frequently. Avoid splashing urine & double flush toilet.
For 23 days: Avoid close contact with pregnant women & under 18s.
Nuclear physician advised me the level of exposure to others was hardly more than the level of background radiation everyone is exposed to every day. The restrictions are precautionary, in case research in 30 years reveal risks not understood or realised today.
I allowed my darling 11 year old dogs to sleep on my bed reasoning they'd be over the rainbow bridge before contamination, if any, could affect them. I discouraged them from licking me though
Ps if your son has TED, RAI can worsen this condition. As others have said, research further.