All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
A baby, means a very young child who has not yet learnt to speak or talk; so if this is what you mean, there is no harm for a baby-girl to touch a baby-boy because they are not yet pubescent. The Prophet said: "The pen is lifted from three……and a child until he grows up [becomes pubescent]." Furthermore, there is no evil which results from them touching each other.
Allaah Knows best.