They may be trying to "sneak" up on you or maybe even their child. I have a few parents who like to see their child in action at dc without the child knowing they're there. If they're spying on you, I can understand that too. How many times do we hear of dc horror stories and often our first thought is " how did the parents not know such and such was happening."

I have a driveway that backs up into a very busy street and we are near traffic lights which makes it even harder to get out. I've had parents park on the side street and walk over for the first little bit until they got used to the driveway or my backlane.

Could be a way to get exercise too lol. Maybe they are those people who park far away in parking lots too?