Hi Natalie, Since I'm still waiting for my 2 yr old Berner's brains to arrive via UPS I'll pass on the "when are they mature" question.
But I can tell you -- 2 dogs is geometrically more work (hair/food/health costs etc/) than 1 dog. So think long and hard about how much time you devote to your single dog and then cube that! Other folks will tell you as well about the pros and cons of multiple dog ownership. I, as the mommy to 3 Berners AND a 19 month old toddler can say that I can't imagine my life with only one dog. We had 2 Berners and added another adult rescue which was fine. But I'm waiting until David is -- oh, about 3 or 4 -- to get a puppy. Puppies can be ALOT of work. As for the kid vs. puppy issue -- it's a tough call. Not to pry, but, is fertility or age an issue for you? If so - go for the baby. But if not, then adding another dog might be a good move now. We adopted a little boy from Guatemala when our Mickey was just over a year old and I'm SO glad that he had had time to bond with us, go through basic obedience training and get housebroken. For us, gettin the dog to a certain level of maturity was important before adding a child. I also would recommend a book by Brian Kilcommons titled, Childproofing Your Dog. It has lots of helpful information on how to prepare your dog for a baby or child. Invaluable. Just my experience, hope the info helps, Catherine Young Madison WI Shadow, Mickey & Jenny