Protesters cuddling teddy bears, eating crisps, wearing pink tutus and banging tambourines have delivered a petition with 68,000 signatures to No 10, calling on the government to scrap plans to introduce standardised assessment for children in reception class.

The “march of the four-year-olds” began in Parliament Square on Thursday with a gentle sing-song and some chalk drawing on the pavement. Then, they ambled hand-in-hand towards Downing Street, where Alex, Safa and Isla – all aged four – went through a line of heavily armed police to hand over the document.

Organised by More Than a Score, a campaign group comprised of parents, teachers and education experts who believe children are overtested in England, the march attracted more than 200 parents, toddlers, teachers and early years experts from across the country, including Durham, Devon, Cornwall, Sheffield, Liverpool and Stafford.

They were protesting against government proposals to introduce baseline assessment in reception classes at schools in England, to test the communication, literacy and maths skills of four-year-olds. Raymond Mensah, from Lewisham in south-east London, joined the protest with his sons Daniel, three, and Joseph, two.

“The test is absolutely out of order,” he said. “It’s not possible to test a four-year-old child. It doesn’t make any sense. They need to give them time, they need to allow the children to grow. It’s too early to test. I absolutely don’t want it.”

Hannah Atkinson, from County Durham, brought four-year-old Oscar and Byron, who is seven months old. “I needed to speak as an advocate for my children because they don’t have a voice. It’s an extra accountability measure for schools, using our children as fodder,” she said.

The 20-minute test will involve each child being taken aside by a teacher, who will conduct the assessment on a tablet. It will take place within weeks of starting school and the information will be used to measure progress throughout primary school. Costing £10m, the scheme is due to be piloted from September and rolled out nationally next year.

The protest was organised by the campaign group More Than a Score. Photograph: Sarah Lee/The Guardian

Some experts have said it is “verging on the immoral” and “deeply demeaning and de-professionalising for teachers”. Parents who are opposed fear it will disrupt a vital settling-in period at the start of school, and could lead to their child being labelled. “It’s an absolute waste of time,” said Angela Roy, from Totnes in Devon, whose daughter Joanie is three. “We should be trusting teachers to do their job.”

Many teachers argue it is impossible to reliably test four-year-olds. When the government trialled reception assessments in 2015, there were complaints that some children became distressed.

Merike Williams, an early years specialist from Stockton-on-Tees, witnessed one of the trials, which were abandoned by the government. “One of the children, I will remember him for ever. He did not answer any of the questions he was asked. He was being a dog. He would go round in a little circle, he would sniff you, then he would sit down and pant. That’s what four-year-olds do,” she said.

A young protester marches on Downing Street. Photograph: Sarah Lee/The Guardian

The government claims the latest iteration of the assessment is not a test, but a way of holding schools to account. “It does not have a pass mark, and there is no reason for parents or teachers to prepare pupils ahead of the assessment, which has been carefully designed with children in mind,” a Department for Education spokesperson said.

“Carried out in the right way, children should not even be aware an assessment is taking place. It will simply provide a vital starting point to measure how well primary schools are doing to make sure all children reach their potential.”

However, campaigners claim pupils in England are among the most tested in the world and that from 2020, they will face standardised tests in reception (baseline assessment), year 1 (phonics check) , year 2 (key stage 1 Sats), year 4 (multiplication tables) and year 6 (key stage 2 Sats).

Maxim, aged four, has it all ahead of him. Stood at the end of Downing Street in his protest T-shirt, he quietly repeated the marchers’ chants into a microphone – “We are little, we are brave, we are more than a score” – while fellow protesters waved their homemade placards that declared “Don’t test me I’m only four”, “Damian Hinds, the Childhood Catcher” and “Kids say, poo poo to tests”.