Hi , treat the evening chic like going to a nice restaurant , no need for a suit especially for the boys. My DH usually takes a jacket for such evening and also if it's a little cooler he has something to wear rather than a sweater. he doesn't take a tie unless he takes a suit!! The boys will be fine in trousers or nice jeans and a shirt (long or short sleeve) or a nice polo shirt.
Ladies tend to wear nice dresses a little dressier than everyday wear or a glittery top and nice trousers.
Hope that is helpful