This past Jan was our first time renting a car, and it was terrific. I will never, ever rely on the buses again. The freedom to come and go was great. No waiting, standing in the aisles, carrying sleeping children, bags, strollers etc. Plus we got our minivan for $192 for 7 days which was cheaper than town car roundtrip with tip and a shuttle to and from US for 2 days.
With the ages of your children, I would recommend it highly. Especially at closing, my younger ones fell asleep in the car every time.