+Francis, of course, is not Jesus. He is Jesus' representative, in a particularly visible way.
As for the child:
Your Holiness, I want to be a priest of Christ, a representative of Christ,
While we are all called, in one way or another, to be a "representative of Christ", some are called to be such in particularly visible ways. Has this child a vocation to the ordained priesthood? Time will tell; may he have the grace to listen carefully to God's call. May God call many holy young men to the priesthood; may He give them the grace to answer that call.
AMEN.