Children and infants are not allowed in the emergency exit rows of airplanes. So it only provides a guarantee that a child won’t sit next (laterally) to you — one might still be behind or ahead of you. If you can find a plane where the exit rows correspond with a change in class or there are multiple exit rows, you might be able to build more of a buffer.
Myself, I find that earplugs or a good set of noise cancelling headphones along with good music or a movie of my choice more than drowns out the world. If you’re really bothered, in-ear earplugs combined with over the ear noise cancelling headsets will give you around 40dB of noise reduction - more than needed for most children.