We've had a lab for quite a few years now. After my wife's lab died 5 years ago, we went and got another one.
The labs we have are GREAT with children - even young children. Just last night our grandson, who is 1 year old, was playing the with dog, lying on her, petting her, etc., and she just loved it. She goes on all of our fishing trips, is great in the boat, loves to play in the water, and is a great companion. I don't think you'll regret the choice of a lab.
I have no personal experience with the Siberian, so I can't help you out there.