The two mobile classrooms quite dominate the playing area of the 270-pupil infants' school.
The first arrived two years ago and the second was put down during the summer holidays to cope with the bulge in the birth rate in Costessey, which is in the suburbs of Norwich.
"Play space has lessened with children at an increasing risk of accidents," said Tony Hull, the headteacher of Costessey (i is pronounced "cossie" as in "swimming cossie" by all those who live there) infants' school.
"You have to be more observant generally to watch where the children are. There are so many corners they can go round.
"Just the sheer numbers we have here puts pressure on all of the facilities we have. Take lunchtime - in 55 minutes we could deal with 200 kids in two sittings. Now we have to have staggered lunchtimes," he said.
The school has gone up from two-form to three-form entry and - despite that - had to turn away 15 pupils from the neighbourhood whose parents wanted them to go there. Every class has 30 in it - the legal maximum for five-to-seven-year-olds.
The bulge in the birth rate is spilling over to the neighbouring junior school (Mr Hull is head of both ) with several classes now up to 34 in size.
It shows no sign of abating, though, if the independently-run pre-school on the infant school site is anything to go by.
It can take 102 under fives - but currently has a waiting list of 25 - set to soar to 50 by January. It had to turn away seven children last Monday because there simply was not enough space for them.
And the parents of those in the pre-school sometimes face the heartbreak of being told there is no room at the infants school for them - after they have been playing within spitting distant of the infants already enrolled for two years.
"Who wants to have to tell a child that - or their mother?" said Mr Hull ruefully.
By contrast, though, the rising class sizes does not present an issue at present - skilful use of the budget with the extra income the pupils bring in allows the school to allocate a teacher and a teacher assistant to every class.
"You can offer a better education for 34 children with a teacher and a teaching assistant than to 25 with just a teacher," said Mr Hall.
The plight of Costessey was highlighted in a report from the Local Government Association which named it as one of the areas in the country likely to face the most acute difficulties in providing enough primary school places by 2016. Two-thirds of all councils are expected to have more pupils than places by then.
A major new housing estate is under way in the area and, said Mr Hull, the area is attracting a large number of migrants - particularly from easter Europe. During the school holidays - and after all the painful decisions had been taken as to who was to get in - another 10 families arrived in the neighbourhood wanting their children to join the school.
Norfolk County Council says many of its urban areas will see a growth in the next few years and acknowledges that Costessey is one of them.
Both the infants' school and the junior school are now academies - the infants' school converted this year - and Mr Hull and his governors believes the problem could be solved by merging them into a primary school and moving the infants lock, stock and barrel to the junior school site.
It is much bigger and would have the space for the necessary extra classrooms.
"You could bulldoze the site and sell it off for, say, residential development," he said. That would provide the funding for adapting the junior school site which could also house the pre-school for the under fives.
Alternatively, the vacant infants school site could be developed to provide a facility large enough to cope with the extra demand it faces. Any surplus money, he and the governors argue, could be retained by the county council.
It is not as simple as that, though, he added, as both schools are academies and now lease their premises from the county council and have had to pledge to hand it back to the county council in its original format.
There are signs, though, that - given time - a way could be found round that.
"We're very sympathetic with the long-term ambition to bring these schools together on a single site in order to help meet the potential future demand for places in Costessey which we expect will increase in the future," said Alison Cunningham, adviser for schools organisation at Norfolk County Council.
"But clearly that is a major project and it would be subject to many factors including funding and planning permission so it simply can't be done quickly."
Meanwhile, the pupils at Costessey Infants' School - as with those at many others up and down the country - will have to negotiate their way round the mobile classrooms as they play in their playground.