Just a thought- there can be the conflation of the idea of a serious, committed, knowledgeable disciple with someone in the position of discipleship- someone perhaps just initiated into a discipleship, or who is interested on some level, following a teacher, exposed to a teacher, etc. In Scripture, some named specifically as Jesus’ disciples were a chapter or so later saying he was possessed by a demon, and in another place they left him.It requires a commitment to the system / teachings / person that one is a disciple of.
Being a disciple is an active thing. It's not a passive thing. One has to work at being a disciple.
It's quite illuminating to read up one what "discipleship" meant in the context of 1st Century Judaism. One didn't just become a disciple because someone taught things at you.
An infant is initiated into this life of discipleship by baptism. They are willing disciples and continue on willingly as children, because God made them that way, to desire to follow after their parents’ ways (in general of course, ha!) Only later in life will they prove to have become disciples who will love and continue with Christ, or among those leave him and so end their discipleship. But there is absolutely nothing strange about the idea of a parent putting his child into a discipleship situation or position as an infant. God claims that infant of believing parents, does he not.
It comes down to what baptism is to show forth, and what’s being said in baptism, and who’s saying it.