Most of the time you'll talk to the police and tell them everything you saw and that's that. It's not likely the police will target you, but that's cold comfort if you somehow end up on the wrong end of a police investigation, which is the point of the video.
You sound smart, what are possible alternatives here? Call in an anonymous tip maybe, or describe exactly what you saw, then refuse further communication without counsel present.
Look, I'll admit I'm biased (I'm a criminal defense attorney.) That said, you never know which good, wholesome, moral conversation that you have with the police will turn you from a heroic savior into a criminal suspect.
(For what it's worth, I'd speak to the police in your scenario. That said, I wouldn't fault anyone for not doing so.)
"Which direction did they go?!?" "Which house is on fire?!" "Does he have a gun?!" are very different questions (with different moral obligations) than "What are you doing in this neighborhood so late at night?" "Do you live around here?" "Is this your car?"
Non-urgent questions and statements should be given in the presence of an attorney, recorded, and preferably on the condition of immunity :)
They reach the intersection, where you get a good look at the men as they turn the corner. The drive halfway down the block, and turn into a driveway, pull into the garage at that house, and close the garage door, and then come out with the baby, and get into a car that was waiting in the driveway, and leave nonchalantly. You recognize the make and model of the car and are even able to read the license plate and memorize it.
You are the only witness to this part of their getaway.
The police quickly come, and ask you if you saw them men and were they went.
Are you REALLY going to say nothing? Or tell them you won't say anything without your lawyer present?