This is from the website. I believe it is still only $20 for less than 24 hrs. It depends on who you get at the border if you are going to have to pay. I know that isn't how it should be but that's what happens. Even groceries they can be very frugal and make you pay duty if they want. Your children get an additional $20 too, so if you want to spend more and not pay duty bring your children
What are your personal exemptions?
After each absence of 24 hours or more
You can claim up to CAN$50 worth of goods without paying any duties. This is your personal exemption. You must have the goods with you when you arrive in Canada and you cannot include tobacco products or alcoholic beverages in this exemption. If the goods you bring in are worth more than CAN$50 in total, you cannot claim this exemption. Instead, you have to pay full duties on all goods you bring in.
After each absence of 48 hours or more
You can claim up to CAN$400 worth of goods without paying any duties. You must have the goods with you when you arrive in Canada. Although you can include some tobacco products and alcoholic beverages, a partial exemption may apply to cigarettes, tobacco products and manufactured tobacco. See the sections called “Alcoholic beverages” and “Tobacco products” for more details.