Chazal (Chagiga 3a) ask why did the infants come and answer so to
give reward to (the parents) who bring them.
From this answer, it seems, there is no benefit for infants who
don’t understand
to listen in, to the learning. Otherwise, the simple answer would
be
they came to listen so to have the Torah absorbed in them.
How do we explain Chazal ( Yerushalmi Yevamos 8b) The mother of R.
Yehoshua brought him in
his crib (infant) into the Bais Haknesess so his ears will
be attached to Torah.
