How can I permanently disable Spotlight Search in ios 10?

I would like to permanently disable spotlight search on my son's iphone 5C running ios 10. Does anyone know if this is possible? Unfortunately even though I have all web browsers blocked, the spotlight search feature will still bring up graphic small thumbnail pics even though the links to them do not work. For example, a search for the word "breasts" brings up a thumbnail pic of just that. I have turned off the spotlight search feature, however since it can not be disabled under "restrictions" it can be turned on and off by the user at will. Is there a way to permanently disable these feature?