[Jaymoss]

I would say it would be possible. As it is for kids and nothing heavy using the existing beams should be fine. Maybe bolster the beams with sections between them to spread the weight. You will have to see what is up there and how you will make the frame but I imagine it should be quite a simple job. Lighting should be easy enough to spur up there too and running an extension for mains through the hidden entrance would be easy. Sounds fun

Look forward to seeing the results