Onomatopoeia is the creation of words that imitate natural sounds. Example: crack, splat, boom etc.
Here are some of them...I don't know if I covered them all but oh well. I think you've got the idea what the examples of onomatopoeia are now.
1. mewling and puking in the nurse’s arms
2. Sighing like furnace, with a woeful ballad
3. And whistles in his sound
4. And then the whining schoolboy
5. lean and slippered pantaloon
6. bearded like the pard