the road that take you to blyth pier from the beach.
dont turn into the pier car park, stay on the main road, head north towards the town centre. you will pass the ridley park hotel / pub on your right, then a big park, take the next right after the park. stay on that road and it takes you to the south side of the harbour. the jettys are all new and safe to fish, the bottom is clean and you should loose any gear.
you can either fish at the start of the jetty, next to the big silver railings were they keep the lifeboat, or drive up a bit, over the small roundabout (big statue piece of crap on the right) carry on driving up that road and you have the main harbour, where you can fish out of the back of your car if you wanted.
you can get some nice cod when the sea is rough and the fish have been pushed up the river, you also have the chance of some really nice flatties, stinking eels and coalies. the kids can try just down the side for small stuff.
2 hooks and a rolling lead with rag or lug normally work well
if you want to try a change in the future, you can go over to cambois, drive towards the pier over the mud track next to the big orange storage tanks, there are a few jettys over there that you can fish off, i always got stonking big flatties when i was a kid over there off the north jetty.
both sides of the river are safe to fish as long as the kids dont stand right on the edge as there are no railings, but the edges have big curb stones or timber sleepers on them.
hope that helps mate