Authorities in Russia are investigating the death of a 7-month-old baby boy found frozen on a balcony of an apartment building Sunday morning, Jan. 5, according to officials.

The child was exposed to temperatures of -4 degrees Fahrenheit for five hours in the town of Nikolaevsk-on-Amur in the far-eastern Khabarovsk region of the country.

According to local media, his 40-year-old mother had placed him in a stroller on the balcony so he could sleep in the fresh air.

The mother reportedly then forgot about her son and only remembered he was out on the balcony five hours later.

According to Russian news site Lenta, a preliminary report into the child’s death suggested that the cause was hypothermia.

The region’s Health Ministry advised people to not leave children outside unattended after the incident, the BBC reported.

“Always know where and with whom [your child] is,” the ministry said in an Instagram post.

“Do not pass by if another child is in danger—in winter a child who is lost or injured on the street can very quickly become a victim of low temperatures,” the ministry added.

According to the BBC, taking children outdoors to help them sleep is not uncommon in some countries with colder climates. Parents in Nordic countries such as Finland and Norway reportedly believe children sleep better and for longer when left outside, and exposing children to fresh air can help prevent coughs and colds.