Dee,

Legally speaking, the children of the Earl and Countess of Wessex are indeed entitled to be called Prince and Princess as grandchildren of the Monarch in the male line as per the letters patent by George V in 1917.

However, it was announced when they married that these titles would not be used and that the rank of any children would derive purely from their father's rank as an Earl. This was at the wishes of Edward and Sophie themselves and does not set a precedent for any other future grandchildren of the Queen by her other male children, though of course such are now highly unlikely!

It was a break from tradition, just as it was when Edward was made an Earl rather than a Duke, albeit that the Dukedom of Edinburgh has been reserved for him.

Theoretically Viscount Severn and Lady Louise Windsor could claim their legal rights upon gaining the age of majority but again this is highly unlikely.

They are currently eighth an ninth in the line of succession and will be knocked down the list when any of those above them produce future issue.