Charles,
The
car insurance for these learners will depend on a couple of things. The car that you said they will be driving, is it yours? If yes, will you be adding them as named drivers on your policy? How long will they be learning in that car or most specifically, how long will they be requiring insurance cover?
You've got 2 choices really:
(1) Get an annual car insurance policy for themSome companies will provide insurance cover for a year even if you have a provisional licence. However this tends to be quite expensive and there's only 1-3 companies which accept learners. When they pass their driving test, they will have to stay with the same company though so they will miss out on shopping around for cheaper deals as they will be tied to a one year contract.
(2) Get car insurance only for the time period that they are learningCollingwood is the only company which will insure learners on a temporary basis. You can get for example insurance cover for your niece and nephew for a month and if they require more practice, purchase 1 week additional cover. The benefit from this is that the insurance is under their name which means that should any incident happen, you will not be losing your no claims discount.