The made-up language you share with your sister can be described as jabberwocky, and so can the meaningless babble coming out of a toddler's mouth. The noun jabberwocky comes from a poem by the same name that Lewis Carroll included in his book "Through the Looking-Glass, and What Alice Found There," which he wrote in 1871. The poem is full of colorful nonsense words, including the word jabberwocky itself.