Boris Johnson has insisted the wheels are "staying very firmly on the bus" as his election campaign arrived in the south west of England.
The Prime Minister sang songs, held Rosie the rabbit, failed in a Where's Wally? search and corrected a pupil during a school visit.
While looking at a book featuring the Incredible Hulk, one pupil shouted "he's got boobies", to which the PM replied: "Those aren't boobies, they are muscles."
Labour, Liberal Democrat and climate change campaigners gathered outside the school near Taunton - some shouting for him to leave his post and others protesting against austerity and the Government's approach to the environment.
The PM visited West Monkton Primary School for his first stop in the south west before heading to see the Little Herons Nursery at the school where Rosie the rabbit lives.
Mr Johnson joined in with the Little Peter Rabbit song but did not join pupils in doing the bunny ears action with his hands.
The PM then suggested singing The Wheels On The Bus, remarking: "The wheels are staying very firmly on the bus."
Meanwhile, Jeremy Corbyn has accused the Tories of fabricating figures after the Conservatives claimed immigration levels would "surge" under a Labour government.
As the Tories shifted the focus of the campaign for the December 12 election into post-Brexit immigration, they claimed net migration under Labour "could increase to 840,000 per year".
Home Secretary Priti Patel's view that "immigration would surge" under Labour came from Tory analysis into Labour's supposed proposals for open borders. Asked about the figures during an interview in Dundee, Mr Corbyn said: "I've no idea where they get those figures from. I suspect they just, quite simply, make them up."
Instead, he said he would commit to "a fair immigration process" that respects workers and recognises their need in the UK economy after Brexit.
Freedom of movement would continue if Leave won in a fresh referendum on Remain and a new exit option negotiated by Labour as proposed by the party. But if the UK again voted for Brexit, Mr Corbyn stressed the need for migrants such as doctors and nurses in staffing the NHS.
"What I will commit to is a fair immigration process that recognised the huge contribution made by migrant workers to this country," he said.
Meanwhile, there was confusion from the Conservatives over the party's immigration policy. Ms Patel pledged to "reduce immigration overall" in the press release attacking Labour's plans, but security minister Brandon Lewis later said the Tories would not set "arbitrary targets".