these problems are related. parking cars in the street slows the other cars down - we all know that because we get irritated when we have to slow down. parking in the street is a great, subconscious cue to others to slow their cars down.
Actually parked cars on the street make it more dangerous for small kids that run out to chase a ball. It is very hard to see a small kid coming out from behind a parked car. And a lot of these cars are parked illegally. They are parked to close to stop signs and curves in the street.