Q: How do I disable "Instant Hotspot?"

My kids have an ipad logged into my icloud account.  They watch netflix on the ipad, which is fine, except due to the "instant hotspot" feature, they automatically log into my phone and set up a personal hotspot, destroying my data usage.  I cannot turn off the personal hotspot and changing the password does not disable it.  The only solution I have found is powering off my phone completely.  Surely there is a way to disable this nuisance feature?