Question: What about those kids he had, what happened to them?
Question: Was it all a dream to him? Did he have a vision that his life was going to be like that?
Answer: Mike, as advertised, was Mr. Destiny. When Jim Belushi asked him if he was an angel, Mike replied that when Belushi is about to make a decision, he's the little voice in his head that helps. At the end of the film, when Mike tells the teenage Belushi that everything is going to work out, the kid replies, "What do you know?"
Answer: Like "It's a Wonderful Life" he showed him an alternate life of what could have been.
Thanks then Mike the bartender must have been an angel.
Answer: Nothing, they're from an alternate reality, Jim Belushi was shown a possible future if he had hit that home run. A different life, job, wife and kids.