You may not share your subscription outside of your household. “Household” means the collection of devices associated with your primary personal residence that are used by the individuals who reside therein.
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If you are willing to keep the whole family on a single account, then they'll need their own when (if) they begin traveling to Disney World on their own or making plans with friends who aren't on your Friends & Family List.
If in-park planning tasks will be your responsibility, there is no need for him to create a separate account. Either way, he will have no problem maximizing the magic of his MagicBand+. My husband has his own My Disney Experience account, and we share planning responsibilities on our family trips.