Commentary Par XXXII 46-48

Dante obviously enjoyed rewarding himself for his strict interpretation of the law of baptism in [Inf IV 30], when he agreed with St. Thomas that all unbaptized children will be found in Limbo.  Now he sees a multitude of saved infants, and he dwells much longer on them.

See C.ParXXXI.59 for discussion of the presence of these babes, not as the adults they should become (according to the standard view), but as the babies they were, back in their sweet flesh.  See Nardi (Nard.1944.1), pp. 317-34, for the 'age' of the babes in Heaven and other problems associated with their presence here.