Please can you advise me on whether it is legal for my son who has a learners to drive with a licensed driver and carry passengers. i.e. my other children?
Yes, it is legal, provided the accompanying driver holds a valid driving licence for that class of vehicle which the learner driver is driving, and is sitting in the front passenger seat.
The learner driver, accompanied at all times by such licenced driver, is allowed to carry passengers provide it is done without reward (e.g. without paying for the transport).
Also, a learner driver is allowed to drive on a freeway under the same conditions as mentioned above.
Learner’s Licence & K53
Driving Licence Test Info