A book series by Mary Harelkin Bishop, with the premise that a certain entrance to the Moose Jaw tunnels sends you back in time to Prohibition-era Moose Jaw, when the tunnels were heavily used by smugglers.
The first book, Tunnels of Time, focuses on 13 year old Andrea Talbot going back in time alone, and encountering gangsters and a nice boy named Vance.
In the second book, Tunnels of Terror, she returns accompanied by her 10 year old diabetic brother Tony, and there's a built-in time limit before Tony runs out of insulin and dies.
In the third book, Tunnels of Treachery, Andrea's Chinese-American friends Kami and Eddie Wong travel back in time along with her and her brother, and they learn about the racism that the Chinese faced in that time period.
The latest book, Tunnels of Tyranny, involves Andrea and Tony trying to stop The Klan from getting a foothold in Moose Jaw.