Assuming your children do not have any no claims bonus, the issue is that your Land Rover is a large vehicle and is in a high insurance group. Although your children have had their licences for some years they are still seen as inexperienced, and it is likely that insurance companies see them using your Land Rover as too great a risk.

If shopping around and using price comparison sites has not yielded any success, the best option may be to consider a second car for them to use. A cheap city car will have the lowest insurance group and result in the smallest possible premiums, and also allow them to build up experience behind the wheel and the crucial no-claims bonus. Even if you were able to insure them on your Land Rover, a second car may still work out to be the cheaper option.