As someone who grew up with a Sheltie, I can tell you they are great family dogs, and great with kids. I got my first Sheltie when I was 8, my sister was 4, and my brother was 2. She was wonderful with us, and loved playing with us.
So a couple points on your concerns-
Companionship- A Sheltie will definitely fit the bill on this. They love their people, and they love being around them. Mine have never been lap dogs, but they definitely like to be near me and follow me around the house constantly.
Exercise- If you go through a rescue, they will make sure you are paired with a dog that fits your family and needs. If you only have time for a walk once a day and are really looking for a dog that lays around most of the day, but will play with you and the kids every once in a while, it's possible to get paired with a dog that will do that.
Barking- Again, a rescue, they will be able to tell you how barky the dog will be. And it might just have to be the dog takes a "nap" in his/her crate while baby naps. Seriously though, some Shelties are just barkly little things and react to things like people walking outside. My current Sheltie barely makes a peep inside. It's a different story when we're playing.
Things you should consider-
Grooming. Shelties have long, beautiful coats. It requires brushing once a week, at minimum. If you end up with a dog with not as much coat, you might be able to get away with longer stretches between. But if you get one with a big fluffy coat, brushing is essential. It keeps away mats, it's good hygiene, and it will reduce the amount of hair floating around your house. With two small children, if you don't think you're going to have time or energy to commit to brushing at least once a week, it might not be the breed for you.
Retired show dogs. If you want an older dog, not a puppy, you can see if breeders have show dogs that are looking for retirement homes. Retired show dogs usually have great temperaments and are somewhat calm. They need to be that way for the ring. And retired dogs aren't always really old. Sometimes they can be as young as 5 or 6. It just depends. Breeders will also know if the dog will be a good fit for your family because at that point, they've spent a lot of time with them!