Child's H4 visa transfer to other parent

Our child(15 years of age) is in USA on H4 extension(I797) based on father’s Change of Employer H1 approval which is valid till end of 2024 and the father has stamped visa till the year end. We want to transfer the child’s status as a dependent on the Mother’s H1B(her extension is approved till end of 2025). So, before the child’s current I-94 expires, can the child go for H4 stamping interview by filling DS-160 as a dependent on the mother alongwith mother’s H1B stamping application? If the mother’s visa is approved, will the child be given visa till end of 2025 matching with mother’s H1B extension end?

Yes.

Yes, your H4 dependent visa end date should align with your H1B.