Bohus-Björkö is one of the biggest islands in the northern archipelago. There are many restaurants, child friendly swimming spots, two guest harbours and hotels.
The harbour area has a handful of places to check out including a small convenience shop, a pizzeria and boat club. If you walk north of the harbour, you will find a good swimming spot which overlooks Källö-Knippla which is a superb spot to take a break if only for the view. The swimming spot itself has the usual pier to lower yourself in and small amount of sandy beach which is usually the kids area.
From Björkö you can reach the islands Kalvsund, Grötö, Källö-Knippla and Öckerö by the foot ferry. Tickets and fares by Västtrafik public transport. Free trip with the Gothenburg City Card.