Why was Jessica's voice so magnetic when she was a child?

Like the second sentence at the beginning of "Elf", it is more attractive.

In fact, some of them are post-synthesized. But if parents want to learn or imitate Jessica's voice, they should listen more and practice more.

Jessica may use her abdomen when singing, which will make her voice longer and have a charming feeling. I don't know if it's right, please adopt it ~