I did something similar for the local school my kids go to, these are 9 and 10 year olds. I took some sheets of cardboard, tape and a pocket full of flat steel washers. Once the window was closed off with the cardboard and a 4x4" hole cut in the centre it was a simple matter of changing the washers (on another piece of board) until we got something that worked. The process took maybe 5 minutes and we used about a 20mm hole projected onto a wall about 3 metres away.
The image was bright enough to see after standing in the room for about a minute, this was on a dull overcast day. The most interesting thing about it was the super wide view. It covered the side walls as well as the one opposite the hole.
abe morell does this sort of thing in hotel rooms..
and then there is the portable camera obscura ... like this one :