We went to the Aeroseum when we were there last month. It's a huge underground bunker full of military planes and helicopters and a few lorries. You are allowed to climb up and sit in quite a few of them and there's a flight simulator in a real plane which DS took me up in, it was really fun!
There is a soft play area for smaller kids and a big cafe.
The staff there are lovely, it's full of retired Swedish gentlemen who like tinkering with planes.
We got there by 2 buses from Gothenborg train station, you should ask the driver to let you off at the Aeroseum - there is just a big plane parked on a crossroads in the middle of nowhere to mark it!