Found this:
St. Thomas, a further reason, which is that the supernatural knowledge of glory comes only by means of actual faith, which transcends all natural knowledge; so that children can never feel pain for the privation of that glory, of which they never had a supernatural knowledge. He further says, in the former passage, that such children will not only not grieve for the loss of eternal happiness, but will, moreover, have pleasure in their natural gifts; and will even in some way enjoy God, so far as is implied in natural knowledge and in natural love: “Rather will they rejoice in this, that they will participate much in the divine goodness, and in natural perfections.” And he immediately adds that although they will be separated from God as regards the union of glory, nevertheless “they will be united with Him by participation of natural gifts; and so will even be able to rejoice in Him with a natural knowledge and love.”