It happens every year in the US that people forget a child in a hot car.
It happened in Ireland recently in a terribly tragic case.
If I saw a baby or toddler on his own in a car in Ireland, UK or anywhere, no matter what the weather, I would wait 10 minutes by the car and then call the police. On previous threads on MN this idea has been ridiculed. But the reality is parents DO forget children (the WP article explains it perfectly) and it is up to bystanders to not walk by but call attention to it.
My MIL was dropping my son off to daycare many years ago in Boston. She got out of the car to put money in the meter, leaving him inside. A young man walking by on the way to the bus stopped and said "you aren't going to leave him in the car on his own are you?" I think she thought he was too interfering - she wasn't that bothered though - but I thought he was right.