Blinky Bill, Thats the Brunswick river beside the Mullumbimby rugby fields. Tweed river runs through Murwillumbah...next river north...and it flooded recently. Mullum Looks like a good spot for a stopover....I'd not leave anything unattended though. I work in the area, the smelly hippy's will pinch anything not tied down.
Broken Head is a great spot but you pay a Byron Tax.... Brunswick Heads is a great town, there are a couple of parks there, i'd pick the one right in town as the Highway could be noisy at night for the other two.. plus the pub is closer.
Further South, Lennox head has the park on Lake Ainsworth....freshwater tea tree lake right behind the sand dunes of Seven Mile beach. Surfclub across the road has a cafe or a short walk to town or Pub. I went past there last Wednesday, place is empty....will be chockers on weekends and holidays. For more basic beach camping, the Flatrock campground halfway betwen lennox and Ballina is a good one. Beaches are usually unpatrolled and not super safe for kiddies but rock fisho's and surfers will like it. lots to explore on the rockshelf between tides to keep kids entertained.
I work in byron.....place is full of backpackers and louts year round. Daytime and Bikini weather can make it worthwhile for a daytrip.