At the top of the Unicorn Theatre, there are two windows: a large picture window looking out onto the street below and another, smaller one, at half the height.
The child-sized window is evidence of the careful thought that has gone into creating Britain's first purpose-built children's theatre on London's South Bank.
But such attention to detail comes at a cost: pound;11.8million so far, with another pound;1.2m to be spent before it opens at the end of the year.
Philip Pullman, the children's author and former teacher whose His Dark Materials trilogy was adapted for the National Theatre, has called on schools to help raise the rest of the money.
Visiting the construction site last week, he said live theatre had a unique ability to capture children's imaginations. He said: "Children need an experience of theatre: it's different from anything else that they get.
It's very different from anything on the screen.
"Actors are in the same space as you are, breathing the same air, the same light plays on them as plays on the audience. It's very different from watching videos at home, it's a shared space."
Projects like the Unicorn are needed to free children from the "philistine" Government culture of tests and targets, he said.
The theatre, which will include a 340-capacity main auditorium and a 120-capacity studio. It will be a permanent home for the Unicorn children's theatre company, which was forced to leave its previous bas, the Arts Theatre in Leicester Square, six years ago.
Pupils from nearby Tower Bridge primary school, many of whom had never been to the theatre before, acted as consultants to the design team, ensuring that everything from sightlines to sinks were child-friendly.
Tony Gram, artistic director, said: "Throughout the building we have tried to provide a child's perspective on the world. It is for children and adults, but children are the key to the whole thing."
A fundraising wall inside the theatre will display gold and silver bricks in the names of schools which have helped to raise pound;500 or pound;100 respectively towards its construction.
The theatre is expecting to perform to 100,000 children aged four to 12 every year, as well as running an educational programme.
Mr Pullman, who is currently working on a sequel to his trilogy, said he was considering writing a play for them.