The friends, who are aged between 10 and 14, told crew members they were feeling poorly after taking off from Dubai.
Four ambulances, as well as a rapid response bike and a hazardous materials unit, met the Emirates Airbus A380 when it landed at Heathrow airport.
Most of the children were treated on the runway but 11 were taken to hospital in Hillingdon, west London.
The youngsters had been travelling back from Cape Town, where they had performed together as part of the 64-strong Only Kids Aloud children's choir, which rehearses at the Wales Millennium Centre in Cardiff.
The group sang with multiple Grammy and Classical Brit Award winner Bryn Terfel during their trip to South Africa.
An Emirates spokesman said: "We're providing the affected passengers with all possible support and are working closely with the local authorities to investigate the issue."
