My wife and I got a black lab a year before we got married. She was AMAZING. Brought twins home when she was about 5 years old and she would come and get me if they were crying, sleep in their room when they were taking naps, etc. When they got older she loved playing on the floor with them, playing fetch, going on walks, etc. She was part of the family.
She was 13 years old when we had to put her down, it DESTROYED my wife as she had been around for so many important dates in our life, the kids took it hard as well and for the last couple of years the three of them have put on the full court press to get another one.
I go back and forth on getting another one now. Not that I wouldn't love to have one just thinking into the future after the boys are out of the house and the wife and I want to travel more. Is that selfish? Sure but it is what it is.
To the OP- You have a 4 year old and a 2 year old? Without a doubt that is pretty much the perfect time to bring a dog into the family.