We can absolutely know from Scripture alone that infant baptism is not a valid practice. Scripture is clear that baptism is for a penitent believer. An infant is not able to believe or repent of their sins. Therefore, infant baptism is not valid.
You are making a leap of logic that isn't warranted. Scripture does not say that one MUST HIMSELF believe before being baptized. I am not aware of a Scripture verse that says "a person can't be baptized unless THAT person believes". You are presuming that because baptism is ordinarily described as a ritual that believers go through to enter union with the Spirit, you think that believers ONLY can be baptized. I don't find that anywhere in Scriptures. The Scripture says that entire households were baptized. It is very likely that would include infants, as most families of the day had many children. Therefore, infant baptism is NOT invalid.
Regards