Answer: Infinity
The two children’s best selling books were Chicka Chicka Boom Boom and Chicka Chicka 1 2 3. The first book involved the alphabet letters racing up a coconut tree, but they fell out after the tree weight caused it to bend down. The second book involved numbers climbing up an apple tree, with a certain number saving the day. It was not #8, but number 0. Eight did arrive late though according to the author so I put that important clue in the riddle.
The twist to the riddle (when I changed the author's plot some) was that I had this item (8) fall off the tree, as seen in the riddle.. I wanted the puzzle solver to imagine it got squished and lay on its side then, to create the answer: infinity. So that was the harder way to solve. The easier way to solve may have been just to look at the riddle and to see the answer may have involved counting, and after combining them with words “boundless” and "eternity”, in the riddle, that could have resulted in an “infinity” guess and correct answer too.