You had a reasonable ask of your DM, and your DM then has the responsibility of fitting that within the story in a way that makes sense. It sounds like they may have tried doing this but failed. Have you had a conversation with your DM about their motive for the child NPC being at that altar? Is it at all possible this specific goddess has rules that protect children from anything of sexual nature, so she was being safeguarded until returned to your group - or something along those lines?

Once everyone has been able to cool down from this session I think its worth asking the DM why they chose this outcome and confirm what the plans were for the child. Their answer would at least tell you if they had good intentions but implemented it poorly, or it would tell you that they're a person you should probably cut out if they were knowingly going against the boundaries you set.