An requirement of installing in new cars a safety mechanism against leaving small children alone in vehicles

I'm not sure how this issue looks in other contries, but in Poland every year there are reports in media about deaths of small children left in car during the hot days.

I'd like to propose additional requirement for all new cars to provide a proper safety mechanism to help save lives.

It should not be hard to implement this as, for example, an  use the backseat belts check of occupied seats to ensure a  proper reminder for the driver, that there is someone left on the backseat.

Additional  technical requirements, like

- the way of communicating this to the driver (with blinking controls/lights or sounds)

- correlation between locking mechanism and seats presure sensors (how to ensure its availability whenengine is off or turn it off when the front passanger seat is occupied)

should be discused with the vehicles producers/importers.

Small children should never be left alone in locked car. 

Probably it can be introduced as an software update even  for older models (2015+) and I'm wondering why this was never the concern of any safety regulations.