One of the improvements which do great honour to modern times and clearly indicates progress is the way in which the insane are now treated and cared for. The maxim which has emerged is to see at last human beings in the insane, and to treat them as human beings like ourselves. The same progress, worthy of the highest accolade, is taking place in the education of children. The age of reason is being recognised at an earlier and earlier age. I have no doubts that we will eventually discern a flash of intelligence in the first smile a baby gives its mother. In this way we will greatly perfect the valuable art by which the child's and the adult's reason can communicate with each other. A common language will be attained for mutual understanding between adult and baby.
[Antonio Rosmini, The Philosophy of Right, Volume 2: Rights of the Individual, Cleary & Watson, trs., Rosmini House (Durham: 1993) p. 18n18.] This is the earlier passage, and as far as I can tell so far, the first mention of the idea. It's interesting that it is also here associated with pedagogy.