Rescue workers said the bodies - 52 children, 33 women and 7 men from Niger were found near the Algerian border.
Many of the bodies were in an advanced state of decomposition, and some had been partly eaten by wild animals.
They were buried in a mass grave, close to where they died.
Authorities said 19 of the group reached Algeria by foot and were returned to Niger.
Two survived after walking the 50 mile trek back to Arlit, a mining down in Niger, and it was there that the alarm was raised.
Niger is ranked by the United Nations as the least developed country on earth. Every year thousands risk their lives by crossing through Northern Niger into North Africa and across the Mediterranean into Europe.
Most of those who make the perilous journey on ancient open-topped trucks are young African men in search of work.
Rescuers said the doomed convoy of women and children was puzzling.
Almoustapha Alhacen who lives in Arlit, a mining down approximately 50 miles from where the bodies were found, was alerted after survivors reached the town on foot. He said:
This is extremely difficult and the most horrible thing I have ever see.
These are women and children; they were abandoned and left to die.
We found them scattered over a large area, in small groups. Some were lying under trees, others exposed to the sun. Sometimes we found a mother and her children, some of the bodies were children alone.
They were left there for so long that their bodies are decomposed.
Unidentified gunmen opened fire on a prison in the centre of Niger's capital Niamey, according to Reuters.
Ila Yaye, who lives near the prison, told Reuters: "We were sitting there when we saw these armed men start to shoot at the guards from the civilian prison. I saw several of them fall and not get back up."
The attack comes a week after al Qaeda-linked fighters launched twin attacks on a military base and a French uranium mine, witnesses said.
Martin Dawes, Regional Spokesperson UNICEF West and central Africa said: "There is still time to avert a catastrophe amongst children inthe Sahel region of West Africa.
"1.1 million children over the course of this year will need life saving intervention because of severe acute malnutrition. This is a crisis with multiple causes where adults will suffer but children will die.
"5,200 nutrition treatment centres have been set up in nine countries but the next two month will be extremely hard for children and their mothers. Most at risk are those who become malnourished and fall prey to conditions such as malaria and diarrhoea."
ITV News has visited a hospital in southern Niger to give an eye-witness account of the food crisis developing there. Africa Correspondent Rohit Kachroo shows in his report how a once-in-a-generation hunger crisis strikes the children of Africa.
Britain is now helping a total of more than 1.6 million people at risk of hunger across the Sahel, the Department for International Development said.
Britain announced £10 million of funding earlier this year to support over 400,000 people across the Sahel region.
International Development Secretary Andrew Mitchell announced in June that Britain will give £10 million additional funding to UN and NGO agencies to provide food, healthcare, water, sanitation facilities, seeds, tools and livestock support for up to 1,027,000 people.
Britain has now announced it will provide a further £5.4 million of funding to the UN and NGOs.