It's around a 70 minute drive from Ross Beach area to the MetroCentre and the MetroCentre will be absolutely heaving because it's the summer holidays and the weather is rubbish. Unless your DC are mega-bored I'd give it a swerve.
I agree. If you really wanted to go shopping I would drive down to the Park and Ride at Kingston Park and get the metro down to Haymarket and visit the shops in Eldon Square.
Another suggestion is the Saturday and Sunday markets at Tynemouth Station. It is a bit of a trek from where you are staying but hey are brilliant. DD (23) lives in Newcastle and it is one of her favourite things to do. Tynemouth is lovely anyway. Morpeth has a number of shops and IMO is better for a mooch around than Alnwick for shopping.
DH is from Northumberland so I have a list of various things to do and places to see here:
Northumberland Attractions* *
Towns
Alnwick, Amble, Berwick upon Tweed, Corbridge, Hexham, Morpeth, Rothbury, Warkworth
Castles
Alnwick Castle and gardens, Aydon Castle, Belsay, Bamburgh, Chillingham, Dunstanburgh, Lindisfarne, Warkworth
Stately homes
Cragside, Seaton Delaval, Wallington – all NT
Other Attractions
Brinkburn Priory, Coquet Island, Coquet Valley, Corbridge Roman Town, Farne Islands, Grace Darling museum, Hadrian's Wall - Chesters, Housesteads and Vindolanda, Ford and Etal, Hauxley nature reserve, Heatherslaw Light Railway, Holy Island, Howick gardens, Ingram Valley, Kielder, Warkworth Hermitage, Woodhorn museum
Beaches
Alnmouth, Bamburgh, Beadnell, Boulmer, Cocklawburn, Cresswell, Druridge Bay, Embleton, Holy Island, Low Newton, Longhoughton, Newbiggin, Seahouses, Seaton Sluice, Warkworth,
Children
Northumberland Country Zoo, Northumberlandia, Whitehouse farm centre