Is it just an visit with parents/ partners/ aunties/ various others all in attendance or is there some sort of assessment there?
If it's the former, I would suggest business casual/ semi-formal. Open shirt with relatively formal trousers and shoes for example.
If there's an assessment/ interview, I'd go a bit more formal with a suit and tie.
Allert is very right though. It's always better to go more formal than less. It's pretty easy to slip off a tie and jacket if overdressed. It's a bit more difficult to dress up if you're in shorts and a t-shirt.