When baptism is performed by immersion, it means that the person is submerged beneath the water. Obviously, this type of baptism is not appropriate for infants. As for dipping the baby’s bottom into the baptismal font, the liceity and validity of such a practice are highly questionable, so much so that I would contact the diocese and ask if a conditional baptism needs to be performed. In baptisms performed by pouring or sprinkling, water should be poured or sprinkled over the baby’s head.
Baptism is such an important sacrament that, in some ways, “creativity” with the baptismal liturgy is even worse than “creativity” with the eucharistic liturgy. This is because baptism is a one-time sacrament that is the gateway for the reception of all of the other sacraments and is ordinarily necessary for salvation.
