Everyone in the congregation making the sign of the cross on the child’s forehead is not following the liturgical book. It has in Baptism for Children:
“41. … He signs each child on the forehead, in silence. Then he invites the parents and, if this seems appropriate, the godparents to do the same.”
(From The Rites Volume One, Liturgical Press, 1990, ISBN 0-8146-6015-0, page 378).
It has the same for the baptism of one child, in n. 79. For a large number of children the celebrant makes a general sign of the cross, and from n. 111 “Then the parents (or godparents) sign the children on their foreheads.” Similarly when a catechist administers the rite, in n. 136.
So it is not being faithful to the liturgical books to have a procession of people making this cross on the forehead. It undermines the special role and responsibility of the celebrant, parents and godparents.