A Syrian boy, aged 1, has died in the forests around the border with Belarus, a Polish aid agency said.
The Polish Emergency Medical Team, a group that operates in the world’s disaster zones, said the child was with his parents when he died on Thursday.
An exact death toll for migrants on the chaotic border has been hard to collate, partly because of limited access to journalists and humanitarian groups.
The group said the boy died early on Thursday after its staff had found the family suffering from dehydration.
“Around 2.26am we received a report that at least one person needed medical assistance,” the charity tweeted.
“When we arrived on the spot, it turned out that three people were injured. They had been in the forest for 1.5 months.
“The man had a lacerated wound to his arm and the woman had a stab wound to her lower leg. Their one-year-old child died in the forest.”
The group provides humanitarian, development and medical relief around the world, including after earthquakes and in areas where there is limited medical expertise.
A humanitarian crisis has developed on the Polish-Belarusian border over the past week after months of simmering.
Poland and the EU accuse Belarus of stoking the border chaos by sending more and more migrants to the border in retaliation for sanctions imposed against Minsk.
Warsaw has pushed back thousands of asylum seekers approaching its borders after passing new legislation in mid-October, contrary to international law and convention.
About 20,000 border police have been sent to the Polish frontier and pleas for help have gone out to the UK, EU and Nato.
Poland in September introduced a state of emergency on the border. Journalists, aid agencies and even volunteer medics are forbidden from entering the three-kilometre buffer.
Hundreds of Iraqi migrants were flown home from Belarus on Thursday after failing to cross the border into the EU.
Passengers on the repatriation flights told of the dire circumstances at the border but some said they would try again to reach the EU.