Harry will begin his UK visit alone on Monday after plans for Meghan, Archie and Lilibet to accompany him collapsed over protection concerns, though they could still join later.
Ravec, the government committee that decides state-funded security, again refused Harry's request, and he has said his children cannot safely travel to Britain without official protection.
The trip starts Tuesday with charity events tied to the Invictus Games, but attention is also fixed on a High Court ruling the same day in Harry's privacy case against the Daily Mail publisher.
The security dispute has shadowed every UK visit since Harry and Meghan left royal duties six years ago, straining already tense family relations as Harry says he wants his children to know King Charles, 77.