The refugees from Syria, Afghanistan and Bangladesh were huddled in a confined space, and the children were already in poor health.
A 29-year-old Romanian man was arrested after trying to escape when he saw the blue lights of the police car.
And three Bulgarians and one Afghan have appeared in a Hungarian court after the discovery of the bodies of 71 migrants packed on a truck in neighbouring Austria.
The men were led into the court in the city of Kecskemit on leather leashes, flanked by police, their faces shielded by manacled hands.
The Bulgarians were aged 29, 30, and 50; the Afghan was 28. Police believe they are low-ranking members of one of the gangs that earn large sums transporting people through Greece and the Balkans.
This Western Balkans route is now one of the busiest ways for migrants trying to reach the EU, second only to the Eastern Mediterranean option.
The smugglers are part of a vast international syndicate that has been the subject of multiple criminal investigations, a European law enforcement official said.
Rob Wainwright, director of Europol, said his organisation and national enforcement agencies were working urgently to catch the ringleaders of an operation that epitomises the rapid expansion and increasing sophistication of human smuggling networks across the continent.
"It was a direct hit in our systems," said Wainright. "We were able to make intelligence connections with many other cases that we're currently working on across Europe."
The abandoned truck, found on Friday beside an Austrian motorway near the border with Hungary, held the decomposing bodies of 59 men, eight women and four children, including a girl aged 1 or 2, all thought to be Syrians.
Kecskemit was chosen for the hearing because it's believed the truck left from the town, 95km north of the Hungary-Serbia border. "We believe it travelled down to Hungary's southern border, picked up the migrants and drove into Austria," said Gabor Schmidt, a public prosecutor.
The four suspects are alleged to be the owner and drivers of the truck. None has yet been charged. If convicted of human trafficking and torture, they could face up to 16 years in jail.
During the hearing, Schmidt asked the court to detain the four men for a month. The court agreed and may extend the 30-day period. Prosecutors said the length of the detention was made necessary by the exceptional nature of the crime and the deaths of the smuggled people.
The suspects are also expected to face separate charges of manslaughter in Austria.
Post mortem examinations were carried out on Saturday in Vienna. Police said the people could have been dead for up to two days. The doors to the refrigerated truck, which formerly belonged to a Slovakian poultry firm, were locked and bound with cables.
Oesterreich, an Austrian newspaper, calculated that the 71 were crammed into 14.8sq m of space. They would have asphyxiated in just over an hour, the children dying first.
Martin Schulz, the president of the European Parliament, accused some EU countries of playing an "undignified game" over the argument about how to distribute refugees among European countries.
"We are not dealing with a failure of the EU, but rather with a glaring failure of some governments who don't want to take responsibility," he told German newspaper Die Welt.
Schulz said some countries which "don't care about European integration" had prevented agreement on a Europe-wide plan to tackle the crisis.
- Washington Post-Bloomberg
