Little Helper Tower, my modification
My daughter sent me a copy of your plans for the Little Helper Tower with the question, "can you make this?", to which I said a hesitant "yes. I decided to modify the plans so that instead of just making two ladders and holding them together with 6 sticks of wood, to make the sides also with vertical 1x2s, then use barrel nuts and furniture bolts to hold it all together. This gives you four pieces and a platform once it is disassembled should you ever need to take it apart.
I took some rough African Mahogany and Sapele and planed it to thickness (3/4") then cut to the required dimensions (1x2, 1x3, etc). I used a biscuit joiner to make slots and then glued the horizontal pieces, using the wooden biscuits, to the vertical pieces. I could not get myself to attempt lining up dowel holes, which would be a stronger attachment. I know this is not the best for a vertical application, but I used Titebond II wood glue and am confident it can take the weight of my grandson.