Bernese Mtn Dog
Siberian Husky
AK Malamute
German Shepherd

We're looking for a dog who:

+ will be even tempered and good with children ~ we understand that there's training on both sides of that equation

+ loves to run

+ can be trained to pull a wagon/sled

+ is strong enough to ENJOY pulling a wagon/sled bearing roughly 60 pounds of children (2 kids) while running next to Mom

Any ideas?
Do any of the above breeds sound right for this?
Am I whacked for imagining this?

Thanks