I grew up Southern Baptist and it was common for people to be re-baptized if they had doubts or left the faith after their first time. The theological justification is that they must not have truly accepted Jesus into their hearts if the first baptism didn't "take," so if you asked to be re-baptized the pastor would ask you a bunch of questions to make sure you're actually serious this time.

I was baptized when I was 7 and have since left the church, but some of my family have begged me to come back and truly accept Jesus into my heart so I can be re-baptized.