This was on so often from around 1979 up until the late '80s that most people may well recall it. It was highlighting the dangers of leaving the front door open when there are young children in the house, and featured a harassed mum coming in from paying the milkman, when she suddenly remembers 'eggs!' and goes back out again to get a dozen, leaving the front door half-open.
Her curious toddler son soon follows her out- cut to mum chatting to the milkie by his float; she starts to get worried when she sees the dog has got out and is sniffing around the front gate. Then everything happens at once; child dashes impulsively into the road into path of oncoming car, Mum screams 'MIIIIIND!' and there's a sickening thud. The ad ends rather dreadfully, with a slow-motion shot of the eggs smashing on the road as a metaphor for what's just happened to the poor lad's head.
It was a horribly effective public info. film, nobody who saw it ever took risks with their children's safety at home again. It must have been seen by generations of young families.