As the video shows, I built a climbing frame.
The box was there so that my father-in-law could have a try at doing a pull-up. He did about half of one which impressed me. Sapphire couldn't reach the bar even on the box or climbing on the clamps that stop the braces slipping sideways, but she was close, then Lynette suggested she put her feet on the brace retaining blocks and that let her get a handhold and she was off.
She had one minor mishap on the way down that saw her collect some scrapes when she didn't pay enough attention to her footing. That made her more careful, so it was useful.
Until the video she had climbed up, sidled her way hand by hand across the bar and got down the other side. This time she decided to get more adventurous and come back again. Little show-off. She's got a partial pull-up too and a fair kip that she copied off me.