The b's are all alliterations. Alliterations are created when the words all begin with the same letter. Alliterations are used to add character to the writing and often add an element of ‘fun’ to the piece.It also helps the structure of the text and adds rhythm

could you rewrite this like a 12 year old but keep it formal

The b's are like words that are best buddies because they start with the same letter, which is super cool! Alliterations make writing more interesting and fun because they give it some extra personality. They also make the text sounds smoother and have a nice beat to it!

make it slightly more formal

Alliterations, my friend, occur when magnificent words mingle in harmony, commencing with the same letter. These delightful linguistic arrangements embellish writing by infusing it with added character and a sense of amusement. Moreover, alliterations confer structure and rhythm upon the text, elevating its impact.