This is where I am interested. I interpret that as Prince Edward's children, who are, or at least one is under-aged, currently receive protection until their 18th birthday. This protection may be RPO or sponsored via the Queen from the Duchy of Lancaster.
If this is the case, I completely understand why Meghan is beside herself regarding security for Archie. Technically, Louise and James are HRH Princess and Prince of Wessex, as stated by Sophie in an article last year. So, this makes sense in regards that without a HRH and princely title, Archie would not receive protection, which was reported as the case when the Sussex family went to Africa.
I truly, truly, truly hope this isn't the case. Because if so....