Tebay services in Westmorland are amazing - I think this might possibly be the nicest service station in Britain. We drive to the Dumfries area every year with two young children. Our two are not great at long journeys so we prefer to split the journey with an overnight stop. We sometimes camp in the Lakes, sometimes we stay in a cheap hotel, or stay over night with friends. This year we are stopping off at Thomas Land (not my idea!). Good luck - Galloway is well worth the long drive. It's beautiful!