On the contrary, it would be the best thing you could do for a baby. Baptism is a grace from God, not something we do for God. Grace does not depend on our intellectual achievements any more than it depends on any other human achievement. This is one of the many ironies inherent in opposition to the ancient Christian practice of infant baptism. To refuse baptism to a baby on the grounds that "the child isn’t able to understand what is happening" is to presume that God gives grace only to those who are smart or old enough to figure out how to get it. This is an implicit assumption of salvation by intellectual works specifically condemned by Scripture and Catholic teaching.