But there are challenges. Here we're talking about single shot cameras using photographic paper. Roll film cameras have a few additional challenges.
If the general population has any thought about pinhole photography, it probably consists of the camera being made out of an existing container using photographic paper as a negative. It's probably a Quaker Oatmeal Box. These became popular as cameras because of the way they were opened. The package consisted of a cardboard cylinder which was completely closed tightly fitted with a second cylinder inside it. To open it, you pulled a string which divided the outer cylinder about an inch or two from the top. The inside cylinder remained intact. This made a nice tight fitting top which was pretty light tight when replaced. There are still directions on the internet which assume you can find oatmeal boxes like this. Oatmeal boxes today however have a plastic lid on top, which is nowhere near opaque.
35mm film used to come in light tight black containers that made spiffy, miniature cameras, but now they're all clear.
One important characteristic of a camera is that it's flat black inside. For one, the material might not be totally opaque, and painting it black might take care of that. The other issue is if the white photosensitive paper reflects light back into the camera, and the walls of the camera reflect it again back to the photographic paper, at best it can reduce contrast, and at worst fog the whole thing.
So essentially if your existing container isn't black or very dark inside, you're going to have to paint the inside black. Flat black Krylon is the solution in most cases. The key characteristic is that it dries in about ten minutes. There are other flat black spray paints, but they take hours and probably overnight to dry. But it's a messy step and requires some pretty good ventilation. I have read of people recommending gluing black construction paper to line the inside of the container to accomplish this.
A container that is not light-tight is not a camera. Absolutely light-tight. In the sun. For at least as long as it takes to get to your picture and back to the darkroom. We all worry about it being dark and cloudy on workshop day, but the Sun is a vengeful benefactor. Most problems with light leaks occur when the sun shines on the joint where you open and close the camera to insert and remove the photo-sensitive material.
It also has to be repeatably opened and closed in safelight conditions, which to most people is going to seem very dark.
Cylindrical packages of all kinds are still available to use, but instead of this kind of close fitting top of the antique oatmeal box, they now have plastic lids of one sort of another, which aren't close to light tight.
I've heard of people using tin foil for this purpose, but I've had a little trouble with regular weight foil. Once it creases, it creates cracks so you might get one or two exposures out of a piece of foil, but if you're going to take a lot of pictures, you're going to have to replace it quite often. Heavy duty aluminum foil would be safer. It's also shiny so it's going to reduce contrast a bit as noted above.
Paint cans have light-proof lids, if you're careful about keeping them relatively clean when you're using the paint. Paint stores often have clean empties you can buy.
Forming a sharp image on a curved back is one of those unique pinhole characteristics that is almost impossible to do with a lens. It should be noted to use semi-matte or matte paper for a negative in a severely curved image plane, because the curve can focus the light and project a couple vertical lines on the opposite sides of the image.
It gives a very characteristic distortion to the image where horizontal lines that are straight in the scene are curved in the image, such as the clapboards in this self portrait leaning against the side of my house.
It often seems to me like a gimmick to make a different sort of image but they all end up looking sort of the same. (I feel the same way about displaying negatives.)
It can be put to compositional advantage. Here it kind of frames my head. With careful selection of subjects it can be minimized. Landscapes often don't have straight horizontal lines except for the horizon which will remain straight if the camera is level.
The three inch distance to a 4x5 inch paper is already pretty wide angle (the camera is about four inches from my nose), and the curve makes it almost 180 degrees in the horizontal. Beginners often can't visualize what this will look like ahead of time, so it's something that should be emphasized. Like any wide angle, encourage them to get closer than they might think necessary.
But it is something unique to pinhole and children often are attracted to this kind of funhouse distortion.
If this is something that seems fun to you I've seen all sorts of cylinders used as cameras including toilet paper roll cores and the boxes that Scotch comes in and each one will provides some kind of unique twist to the image.