A session lasts an hour or two. The set takes considerably longer, and it is what decides whether the photographs are any good.
Design
Starts with the child's age, not the theme. What a five-month-old can do and what a two-year-old can do are entirely different problems, and a set that ignores that produces a session of adults propping a baby up.
Then the palette, then the prop list. You see both before committing, which is also when we say if something will not work at your child's stage.
Sourcing and making
Some things are hired, some are bought, and a fair number are made — fabric animals, painted panels, oversized props scaled so a baby looks small beside them. This happens in the week before, not the morning of.
Building
Three layers. Background first, then the mid-ground the child occupies, then the foreground the camera shoots through. That last layer is the one most studios skip because it is fiddly to light, and it is the one that makes a photograph feel like a place rather than a backdrop.
It adds around forty minutes. It is worth every one of them.
Lighting
Set before anyone arrives, and set for the child rather than the props. The most common failure in themed photography is a beautifully lit set with a slightly dark child in the middle of it — the eye goes to the brightest thing in the frame, and it should be the face.
The safety pass
The last step, every time. Nothing overhead. Nothing sharp. Nothing that can be pulled over. Anything within reach either soft, washable, or too heavy to move. Anything a child might put in their mouth is either not there or is something we would not mind them putting in their mouth.
What gets abandoned
Plenty. Ideas that look wonderful in a sketch and turn out to need a child to hold a position, wear something over their face, or stay still for longer than a few seconds. Those get redesigned before the day rather than attempted on it.