If your invitation says "and Guest" then yes, if not, we would prefer it it was just you.
Cocktail/semi-formal/dressy casual. Good choices include a cocktail dress or formal summer dress, a suit and tie or sport coat and dress pants. However, we want you to feel comfortable so if this doesn't work for you don't let that stop you from coming and celebrating in YOUR best.
Our grandchildren will be there but we want our wedding to be your night off so please book that sitter and come enjoy yourself.