Fifty-three children were rushed to hospital in Nairobi after tear gas was thrown into their class by police during protests on Wednesday.
Dr Aron Shikuku from Eagle Nursing Home hospital told the BBC the children were released after being treated.
He said they had suffered breathing difficulties and shock.
There were demonstrations around the country called by the opposition over the rising cost of living, but they turned deadly.
Six people were killed, authorities said.
Human rights bodies however put the number of those dead at 12, with many more injured.
Two people died after protesters set fire to a police station, while another died during an attack on a police van along the Nairobi Expressway on the outskirts of the city, reports say.
The protests had been banned, but people took to the streets anyway, such is the anger amongst some Kenyans about the rising cost of living and a new finance bill – which includes tax increases.
The controversial hikes include the doubling of fuel taxes and the imposition of a 1.5% levy on all employees to fund new houses.
The government says the hikes are essential to pay off debts and create job opportunities for young people but the law has been suspended by a court over constitutional concerns.
Opposition leader Raila Odinga, who was defeated by Mr Ruto in last year’s election, has been pressing the government to reverse the tax hikes, calling for civil disobedience last month and describing those who want to implement the finance bill as “traitors”.
A rally of the Azimio la Umoja-One Kenya Coalition Party had been scheduled for Wednesday, but its leader, Mr Odinga, called it off, saying he wanted to avert further violence.
Policing boss Japhet Koome said on Tuesday that “all lawful means” would be used to disperse the demonstrations, the AFP news agency reports.
These latest protests come just a few days after several people were killed during anti-government demonstrations last Friday, in which human rights groups accused the Kenyan police of using excessive force.
Kenyans are divided over the protests, with some backing them, saying the high cost of living is unsustainable: “Kenyans are personally defending themselves, arguing against the imposed taxes. The salary you are paid against what you are spending, there is nothing important you can do for yourself as a human being,” William Musembi told the Reuters news agency.
While others have complained about looting: “A group of around 400 to 500 people were gathering along the highway and they came all at once and broke the doors that were already bolted,” supermarket manager James Kagimi Wanjema told Reuters.
“They were able to access the tills, they looted some cash and merchandise. It’s a little chaotic, very chaotic,” he said.